Tubeless tyres are pneumatic tires which do not have a separate tube inside. Ordinary tires have a separate tube inside the tire.

Tubeless tires are different in that they have continuous ribs. Integrally moulded, these ribs are sealed due to the pressure because tubeless tires do not need an inner tube, they are safer.

The valve is mounted directly in the rim and and the wheel rim and tire form a perfect seal which is airtight. Tubeless tires are easier to fix if they get punctured as they have a special gel which reseals the tire if the tire is penetrated by a sharp object such as a nail. .

Normal tyres have a tube inside which contains the air on which the weight of  the vehicle is borne.  Tyres which do not have a tube inside them are known as Tubeless tyres.

In Tubeless, the air is held not in an airtube but between the rim and the tire.  Tubeless tires have



When the Air Conditioner is turned on in a car, the compressor starts compressing the system’s refrigerant and its temperature increases. It gives up heat as it is flown through the condenser (that other instrument that stands in front of the radiator and looks like a radiator itself).

The refrigerant gas then passes through the receiver/dryer so that the contaminants and moisture get removed. It then enters the expansion valve/accumulator. Here, the refrigerant is cooled down further so that it loses the pressure and temperature before it enters the evaporator.

The evaporator can be considered to be a mini radiator that gets colder as it lowers the refrigerants temperature more and, additionally, discards moisture from the air. There is a ventilation system’s blower motor in the system that blows air over the cooled down evaporator and sends cool air into the passenger compartment.



Alcohol is superior to gasoline! It has an octane number, it burns much cooler creating less vibration, it is less flammable so accidents are rare and it is 98% pollution-free. Alcohol also has lower evaporative emissions, and no deposits of carbon are left in the engine or oil after it is burned which results in a increase of engine life. Moreover, engines using alcohol as fuel can get at least 20% better mileage than gasoline or diesel.
Alcohol can be used to power diesel engines, locomotive trains, aeroplanes, small utility engines, generators to produce electricity, heaters for heating our homes and to cook our food.

The by-products obtained after alcohol production are clean. Instead of producing waste we get worth more than the fuel itself. These by-products are very good fertilizers and herbicides. The by-products are very nutritious as well.




An airbag system has three components: the bag, the sensor, and the inflation system.

The Bag
Airbags are made from a fine gauge of nylon and it is folded into the steering wheel, dashboard and the door panel. Sometimes, airbags are folded in the roof rails above the door too.

The Sensor
This tells the bag when to inflate. It usually requires a force equivalent to running into a brick wall at 10 - 15 mph. In contemporary airbags, sensors determine whether a person is in the front passenger seat. Sensors may also see whether the passenger has enough mass so that the bag is safely deployed.

The Inflation System
The inflation system is made of potassium nitrate (KNO3) and sodium azide (NaN3). The gas inflates the bag at about 200 mph. The gas is removed through tiny holes in the airbag to deflate. The whole process takes nearly 1/25 of a second. 




Idling is continuing the vehicle's engine to run when the vehicle is not in motion. This usually happens at a red light, waiting, or otherwise when the vehicle is stationary with the engine running. It is wise decision to turn off the ignition if waiting for more than 10 seconds. Restarting the car does not burn more fuel.

In fact, idling a car for 10 seconds wastes more fuel than starting the engine again. It has been proved that letting the engine idle uses more gas than starting and stopping. Contemporary vehicles, when subjected to idling, consume more gas than they do for starting the engine.

So, while the vehicle is parked for a short period of time, fuel is saved by turning the engine off and restarting it. The AAA says a quarter of a gallon of gas is used for every fifteen minutes of idling. So, doing this for five days a week burns $4 worth of gas.



The primary circuit of an engine consists of the battery, the ignition switch, a resistor, an Ignition module or contact points, and coil primary wiring. They are fitted so that the electricity flows continually through them. The primary circuit voltage is usually very low, it is about 12 volts. The wiring has a thin layer of insulation to save from short circuit.

The secondary system of circuitry is made of three basic components: ignition coil, the distributor, and the spark plug. This system is what is used for new formats like the distributor less ignition systems.

Ignition Coil
The ignition coil is made up of two separate cover of copper wire around a laminated iron core. A high-voltage current is produced in the secondary winding that has many turns of thin wire. This high-voltage current flows via the core portions of the distributor.

Distributor
The major duty of the distributor is to allow the current pass from the coil to the correct spark plug at the right time. It has a rotor inside that passes close to the spark plugs.

Spark Plug
The spark plug has to create a high-voltage spark needed to ignite the fuel mixture in the combustion chamber.



In cars, the parking brake is a latching brake generally used to keep the vehicle stationary. It is sometimes used to stop a vehicle from rolling when both feet are engaged.

A number of vehicles have been made with an independent drum brake on the transmission output shaft. It is called a driveline parking brake. This is completely independent of other braking systems. This brake is effective till drive train is intact. This type of parking brake is used by either a foot pedal or a hydraulic cylinder.

The integral brake is a kind of parking brake on the inside of the disk brake system. This system usually has cables to engage the parking brake as the normal drum brake system. There are usually two brake shoes in the rear drum. When the parking brake is pulled, it lets a cable tighten up the shoes so they press against the drum, holding or stopping the vehicle.



An indicator lamp is a type of warning device that alerts the drivers of problems with various parts of their vehicles. Oil pressure, water temperature and the voltage are usually showed on the dashboard indicator lamps.

In case of a dangerous reading from a engine sensor, the indicator lamp starts to illuminate. In fact, most cars produced nowadays have the basic indicator lamps to show potential problems.

For all functions of the automotive engine, a sensor is there to transmit signals to the dashboard. The need of a system of warning lights and indicators is to allow the driver to understand how the engine is operating.

The sensors are usually programmed to send a signal to the indicator lamp when there is a non-standard sensor reading. This signal illuminates the warning light, telling the driver that there is a problem with the engine.



Indirect injection is a type of engine fuel injection where fuel is not directly injected into the combustion compartment. Gasoline engines have indirect injection systems, wherein a fuel injector delivers the fuel.

An indirect injection diesel engine pumps fuel into a prechamber, where combustion starts and then spreads to the main combustion chamber. The prechamber is made to ensure proper mixing of the atomized fuel with the heated air.

The purpose of indirect injection is to speed up combustion to increase the power output by increasing the engine speed. Indirect injection systems have air that moves fast, mixing the fuel and air. This usually simplifies injector design and lets use smaller engines and less tightly toleranced designs. This allows designing of engines that are more powerful yet less costly to manufacture.



In cars, the parking brake is a latching brake that is used to keep vehicle stationary. Parking brake is also used to stop a vehicle from rolling when both feet of the driver is on the clutch and accelerator pedals.

The parking emergency brake is built to operate the rear brakes by a series of steel cables that are connected to a hand lever. The parking brake acts on the rear wheels, when they have reduced traction while braking. In some cases, parking brake is applicable on the front wheel.

In emergency cases of brake failure when the vehicle is moving, the parking brake along with the engine gear system can be used to slow the vehicle down.



The tire pressure mentioned in the vehicle's owner's manual is the recommendation for cold tire inflation pressure. It should be checked before driving a longer distance or before the ambient temperatures rises or the sun's radiant heat inflates the tire more.

Tire pressure is the net pressure of air in the vehicle's tires, expressed in pounds per square inch. It is necessary to check the tires' pressure with a pressure gauge as frequently as possible.

When inflation pressure is too high, then tire touches the ground marginally making the vehicle bounce around on the road. This makes traction suffer and increasing the stopping distances. The ride comfort may also be compromised.
If inflation pressure is too low, the tire's surface area that touches the ground is too vast, which increases friction. The tires will wear prematurely due to this apart from getting overheated.



A Live axle is a type of beam axle. A beam axle is a suspension design, where a set of wheels is connected laterally by using one beam or shaft. Beam axles were common in the rear wheels, but they have also been used as front axles in rear-wheel-drive vehicles.

A live axle is a beam axle where the shaft or the shafts connected to move as a single unit transfers power to the wheels.

The beam axle that is not transmitting power is a dead axle. These axles are usually found in vehicles with Hotchkiss drive. However, such suspension systems are also found in other types of power transmission.

The basic advantage of the live axle is its simplicity which makes it very less space-consuming and relatively cheaper to manufacture. Live axles are almost used in all heavy-duty trucks and most light and medium duty pickup trucks, SUVs, and vans. These axles are almost always found in the rear set of wheels.





Liquefied natural gas is a type of natural gas that has been converted to a liquid. It is predominantly methane in terms of contents. Its volume is about 1/600th the volume of the gas in the gaseous state. It has no odour, no colour, no toxicity and no corrosiveness. The hazards related with LNG include asphyxia and high flammability after vaporization and freezing.

The liquefaction process of the natural gas includes removal of dust, acid gases, helium, water, and heavy hydrocarbons. The natural gas is condensed by cooling to −162 °C (−260 °F); with a maximum transport pressure applied at 25 kPa (4 psi).

In a typical LNG process, the gas is purified by removing water, oil, mud, and other gases. Trace amounts of mercury are also removed from the gas to stop mercury amalgamating with aluminium in heat exchangers. The gas is then cooled down in various stages until it is converted to a liquid.

LNG can be more volumetrically reduced than compressed natural gas (CNG). That is why LNG is more cost efficient to transport.



A light commercial vehicle, as the name suggests, is a relatively light commercial vehicle. This official term of light commercial vehicle is used within the European Union, Australia, New Zealand, and occasionally in both Canada and Ireland. These are also the countries where the commercial van is more frequently used.

Light commercial vehicles are commercial carriers that have a gross vehicle weight of less than 3.5 tonnes. The term light goods vehicle (LGV) can be often confused with Large goods vehicle (also called 'LGV'). The latter is the official EU term used for vehicles that have gross weight of over 3.5 tonnes.

The light commercial vehicles usually are pickup trucks, vans and three-wheelers that are all commercial goods or passenger carriers. The LCV concept was usually devised for a compact truck that is generally ruggedly built. The LCVs are popular due to their low operating costs and powerful yet fuel efficient engines. LCVs are used mainly in intra-city operations.



Wheel alignment refers to the adjustment of a vehicle's suspension that connects a vehicle to its wheels. It is not just an adjustment of the tires or wheels. The key to good alignment is in adjusting the angles of the tires that decides how the tires make contact with the road.

In a nutshell, wheel alignment means adjusting the angles of the wheels so that they make a perpendicular angle to the ground and stays parallel to each other. The purpose is getting maximum tire life and a vehicle that has straight and true tracks when driving along a straight and level road.

If your vehicle tracks like an arrow, the wheels likely are properly aligned. Even so, it is good to check alignment when you have your tires rotated. Don’t forget to align the wheels when you buy new tires so they don't immediately start to wear unevenly.



A car burglar alarm is a security alarm. It is an electronic device used to discourage theft of the vehicle itself, its contents, or both.

Car alarms emit high-volume sounds, such as a siren, klaxon, previously recorded verbal warning, the vehicle's horn, or a combination thereof when there is any security threat or when conditions for triggering an alarm are met.

The alarm may also flash some of the vehicle's lights, and some of these alarms also notify the car's owner via a paging system. There is also an option to interrupt and stop various electrical circuits so that the car is disabled and cannot be started.

Car Alarms can be equipped from the factory itself or installed later.

Keyless remote car burglar alarms are generally based on strong cryptography authentication methods, including Radio receiver, Immobilizer, Motion detector and Wireless USB.



Hydraulic brakes follow a simple principle: forces applied at one point are transferred to other points by means of an incompressible fluid. In brakes we call this brake fluid.

The initial force applied is multiplied in the process by means of increasing the area of application. Therefore, the multiplication is derived by increasing the sizes of the pistons at either end.

 In braking systems, the piston at the end of application of force, driving the fluid is smaller than the pistons at the brake pads. Therefore the force is multiplied many times, helping to brake easily and more efficiently.

Another important characteristic of hydraulics is that the pipes having the fluid can be of any size, length or shape which allows the lines to be fed almost anywhere. They can also be split to let the master cylinder to operate two or more slave cylinders in case of a need.



An air brake or, a compressed air brake system, is a friction brake for vehicles in which applying compressed air on a piston is used to apply the force to the brake pad needed to stop the vehicle.

Air brakes are generally used in large heavy vehicles, especially those having multiple compartments which must be linked into the brake system, such as trucks, buses, trailers and the railroad trains.

The system is made up of service brakes, parking brakes, a control pedal, and an air storage tank. For the parking brake, a disc or drum brake system designed to be held in the 'applied' position by spring pressure is placed.

Air pressure releases these "spring brake" parking brakes. For the service brakes to be applied, the brake pedal has to be pushed, so that the air creates pressure (approx 6.89-8.27 bar) to engage the brake chamber. This stops the movement of wheels.



Tubeless tyres are pneumatic tires which do not have a separate tube inside.
Ordinary tires have a separate tube inside the tire. Tubeless tires are different in that they have continuous ribs. Integrally moulded, these ribs are sealed due to the pressure
Because tubeless tires do not need an inner tube, they are safer. The valve is mounted directly in the rim and and the wheel rim and tire form a perfect seal which is airtight. Tubeless tires are easier to fix if they get punctured as they have a special gel which reseals the tire if the tire is penetrated by a sharp object such as a nail. .  



Automatic guided vehicle systems are robots or unmanned machines used to safely transport all kinds of products without human intervention within production, logistic, warehouse and distribution environments.

AGVs are used to consistently and predictably transport material to places that may be serviced by fork lift trucks, conveyors, or manual cart transport. They are generally used in warehouses where high volumes of repetitive movements of material is required, but only little or no human decision making skill is applicable to perform the movement. They are very useful in serving processes where there is no change is contact and use of barriers - such as conveyors - are undesirable in AGVs.

Application of the AGV has broadened during the late 20th century. AGVs often follow markers or wires in the floor, or use own vision, or magnets, or lasers for navigation within a limited range of transportation.





A catalytic converter is a part of automobiles that uses a catalyst to convert three harmful compounds in the exhaust into harmless compounds.

The three harmful compounds are:

Hydrocarbons (unburned gasoline)

Carbon monoxide ( created due to combustion of gasoline)

Nitrogen oxides (created when nitrogen in the air combines with oxygen)

Carbon monoxide is a dangerous poison for any air-breathing animal. Nitrogen oxides create smog and acid rain, and hydrocarbons create smog.

In a catalytic converter, the catalyst, either platinum and palladium, is coated onto a ceramic honeycomb or ceramic beads that are placed in a muffler-like package on the exhaust pipe. The catalyst converts carbon monoxide into carbon dioxide, hydrocarbons into carbon dioxide and water, and nitrogen oxides back into nitrogen and oxygen.





A diesel particulate filter (or DPF) is a device created to remove the diesel particulate matter or soot from the exhaust gas of a diesel engine.

As with any filter they have to be regularly cleaned to maintain performance. This cleaning process is called 'regeneration' in which the collected soot is burnt off at high temperatures.

Passive regeneration occurs automatically on fast A-road runs when the exhaust temperature is high. However, many cars don't get this sort of use and hence vehicle manufacturers design an 'active' regeneration processor.

When the soot loading in the filter approaches about 45%, the vehicle's ECU will initiate post combustion fuel injection to increase the exhaust temperature to optimum levels and trigger active regeneration.

A regeneration cycle takes place when driving a journey for 10 minutes or so at speeds greater than 40mph.





"Charge-Air Cooler", is an air-to-air or air-to-liquid heat exchange device used to improve the volumetric efficiency of internal combustion engines by increasing intake air-charge density through isochoric cooling. A fall in air intake temperature offers a denser intake charge to the engine and offers more air and fuel to be combusted per engine cycle, which increases the performance of the engine.

In the past, turbochargers were run in stages. The first stage compressor fed the inlet of the second stage compressor which, in turn, would further compress the air before it enters the engine. Extremely high pressure is developed in such arrangements and a charge-air cooler is placed between the first and second stage compressors. That cooler is called the "Intercooler".

Another charge-air cooler is often positioned after the second stage, which is the final compressor stage, and that is called the "aftercooler". An aftercooler is a type of cooler whose outlet fed the engine.



There is a process called incineration or combustion which is actually rapid oxidation that can be used to convert VOCs and other gaseous hydrocarbon pollutants to carbon dioxide and water. Incineration is ideally accomplished in a special incinerator called an afterburner.

An afterburner is generally made of a steel shell lined with refractory materials such as firebrick. The refractory lining saves the steel shell and acts as a thermal insulator. When enough time and high enough temperatures are used, gaseous organic pollutants get completely oxidized, with an incineration efficiency approaching near 100 %.

To get complete combustion of the VOCs and other hydrcarbons, the afterburner must offer the proper amount of turbulence and burning time, and it must also maintain high enough temperature.

Afterburners are generally used to control odours, destroy toxic compounds, or reduce the amount of photochemically reactive substances released into the air.



The air-fuel ratio is the ratio of weight of air to that of gasoline mixed by the carburettor for ideal combustion by the engine. This ratio of paramount importance because there are limits to how rich (with more fuel) or how lean (with less fuel) it may become, and still stay fully combustible for an efficient firing and better engine performance.

The engine can operate with an air fuel ratio that ranges from 8:1 to 18.5:1 i.e. from 8 kg of air/kg of fuel to 18.5 kg of air/kg of fuel.

Stoichiometric Air-Fuel Ratio

It is the ideal ratio at which all of the fuels blend with all available oxygen in the air and be completely burned. An air fuel ratio of about 14.7:1 i.e. 14.7 kg of air/kg of gasoline produce this ratio, but the exact ratio can vary somewhat.



Aerodynamic Drag is the force that opposes an automobile’s motion through the air. Drag is created in the direction of the moving air when the air pressure encounters a solid object. Drag is generally undesirable because power is required to overcome it.

To quantify the amount of drag on an automobile, we use a value called the drag coefficient (cd). This number depends on the shape of the automobile , its speed and surface roughness, the density of the air and the nature of the air flow (laminar (smooth) or turbulent).

Forces that influence drag include the air pressure against the automobile, the amount of friction along the sides of the automobile’s body and the relatively negative pressure, or suction, on behind the automobile.



Fuel additives are compounds used to enhance the quality and efficiency of the fuels. Sometimes, the additive is injected into the gasoline itself; at other times, the fuel additive is added from outside. The aim of fuel additives is to improve or maintain the optimum performance of the engines.

Fuel additives may boost the octane level of the gasoline. This helps the engine derive more power from the same amount of gas. This offers the ability to travel longer with the same amount of fuel.

Engine maintenance is another task of fuel additives. With these types of additives, the focus is on preventing the gathering of sludge and other unwanted deposits in different areas of the engine.

Because of lesser buildup of sludge in the lines and in the various moving parts on the motor, the
engine life is effectively prolonged.

Types of additives range wide and include metal deactivators, oxygenates, corrosion inhibitors and antioxidants.





For a true rolling of a four wheeled vehicle moving on a curved track, the straight lines drawn through all the wheel axes must intersect at the instantaneous centre.

The Ackermann steering uses the two front steered wheels pivoted at the finishing points of an axle-beam. There is an original Ackermann linkage which usually has parallel set track-rod-arms ensuring that both steered wheels swivel equally. Consequently, the projection lines do not meet at one point.
In case both of the front wheels are allowed follow their own natural paths, they would ultimately

converge and come across each other. As the vehicle will have to move along one mean path, so both of the wheel tracks would conflict which may cause tyre slip and tread scrub.

Therefore a modified linkage is used at inclined track-rod arms so that the inner wheel swivels about the king-pin a little bit more than the outer wheel.



Acceptance testing is basically done by the user or customer to establish confidence in the system. In case of automobiles, the vehicle is checked whether it meets certain standards in terms of safety and performance etc.

The types of acceptance testing applied to automobiles are:
The User Acceptance test: is done to test the functionality to validate the fitness-for-use of the system by the user. User acceptance test is done by the users and application managers.

The Operational Acceptance test: is also known as Production acceptance test. It validates whether the system meets the standards for operational reasons. In most of the organization the operational acceptance test is performed by the administrators before the vehicle is released for sale.

Compliance acceptance testing: is done because the governmental, legal or safety regulations must be adhered to.

Various other testing including safety and mobility may also be done as acceptance testing from time to time for automobiles.



For an automobile to get smooth acceleration, advancement in the timing and an increase in fuel flow are required. There is a vacuum distributor in automobile carburettor that senses when you open the throttle and then it provides the extra advance timing. The accelerator pump provides the extra fuel needed for acceleration.

The accelerator pump is usually connected by to the accelerator; when momentary acceleration is required, the pump squirts fuel directly into the carburettor for  increasing the amount of fuel-to-air concentration.

Most carburettors contain a small bent brass pipe pointing straight down it-- it is called the delivery tube. When the throttle arm is pulled firmly, a squirt of fuel flows into the carburettor right from the delivery tube.

This increased fuel increases the power of the engine and the automobile gets an instant acceleration. The accelerator pump must be adjusted suitably for optimum performance, and it is wrong to believe that the more fuel the pump injects, the better it is for the vehicle.



A bumper is a component attached in the front and rear of an automobile to absorb impact in a minor collision, ideally minimizing repair costs. Bumpers are standard components that are commonly used in all vehicles nowadays.

Bumpers have two major safety functions.  They diminish height mismatches between vehicles.  They also protect pedestrians in the event of a collision.

The bumper structure on modern automobiles usually have a plastic cover over a reinforcement bar made up of steel, aluminum, fiberglass composite, or plastic.

Bumpers save other vehicle components by dissipating the impact of kinetic energy generated in a collision. This energy is a function of vehicle mass and velocity squared. In formula form, it is given by  which suggests that a vehicle protecting the components at 5 km/ hr must be four times stronger than the bumper that protects at a 2.5 km/hr.



A shock absorber or shock damper is a mechanical or hydraulic device designed to absorb and decrease the impact of a shock impulses. Shock absorbers convert the kinetic energy of the shock to some other form of energy to dissipate it. A shock absorber is a type of dashpot.

Most used in vehicles, shock absorbers reduce the effect jerks, resulting in improved ride quality and vehicle handling.

There are two major types of shock absorbers: Twin tube and Mono tube.
Twin tube: Also called a "two-tube" shock absorber, this device has two nested cylindrical tubes, the inner, "working tube" and an outer "reserve tube". Twin tube shock absorbers can be basic, gas charged, position sensitive, acceleration sensitive or coilovers.

Mono tube: the mono-tube shock absorber is a gas-pressurized shock absorber that also comes in a coilover format. It is made up of only one tube, the pressure tube, however, it has two pistons.



Sandpaper or Glasspaper are a type of coated abrasive that consists of sheets of paper or cloth with abrasive material affixed to one face. Nowadays, sand or glass is not used.


Sandpaper is produced in different sizes and is used to remove unwanted material from surfaces, either to make them smoother (in painting and wood finishing), to remove a layer of material (e.g. old paint), or to make surface rougher (in gluing).

Types
Backing:  Backing for sandpaper can have clothes (cotton, polyester, and rayon), PET film, and "fibre", or rubber apart from the paper.

Material: Garnet, emery, aluminium oxide, silicon carbide, alumina-zirconia, Chromium(III) oxide, ceramic aluminium oxide can also be used in sandpapers.

Bonds: Different adhesives, such as Hide glue, are used to bond the abrasive to the paper. Waterproof sandpapers use resin bond and a waterproof backing.

Open coat sandpapers have particles that are separated from each other and it is more flexible.



Abrasive Disc is a disc of abrasive material that rotates in a tool such as a sander. Abrasive discs are used usually for use in applications related to blending, finishing and polishing . Abrasive discs use the combination of several minerals, resin systems and backings for better functionality.

This combination results in a wide range of products to meet various requirements for use on materials such as wood, gel coat, painted substrates, metal, composite, etc The discs are generally manufactured using a composite material with coarse-particle aggregate pressed and attached together using a cementing matrix to give it a solid, circular shape.

 Depending on the intended usage of the disc, various forms and cross sections are available. Abrasive Discs may also be built using a solid steel or aluminium disc with particles bonded to the surface. Most abrasive discs are artificial composites of artificial aggregates, but initially natural composite stones (millstones) were also used



An Abrasive Cleaner is a type of mechanical cleaner that physically removes dirt, stains and tarnish the surface.  They are made up of particles or physical abraders and use friction to remove the dirt stains etc. Physical abraders include materials such as sandpaper, scrubbing,  padsteel wool.  Abrasiveness usually depends or coerciveness of the used material.

Depending on the harshness, there are three types of Abrasive Cleaners.

Mild Abrasives such as fine plastic mesh pads, soft brass wool, nylon coated sponges, rotten-stone and whiting are often used to clean pots and pans, interiors of ovens, and drip pans.

Examples of Moderate Abrasive Cleaners are fine pumice and fine steel wool. Steel wool has grades from 0000-super fine, 000-extra fine, 00-very fine, 0-fine, 1-medium, 2-medium coarse and 3-0 coarse.

Strong Abrasives are the strongest among abrasives. Examples include medium and coarse steel wool, metallic mesh cloths and balls, metallic brushes, coarse pumice, and sand/silica etc.