the tank. After the sheet is cut to the shapes needed, various pieces are bent to create the basic shell and/or ends and baffles for the tank. Many fuel tanks' baffles (particularly in aircraft and racecars) contain lightening holes. These flanged holes serve two purposes, they reduce the weight of the tank while adding strength to the baffles. Toward the end of construction, openings are added for the filler neck, fuel pickup, drain, and fuel-level sending unit. Sometimes these holes are created on the flat shell, other times they are added at the end of the fabrication process. Baffles and ends can be riveted into place. The heads of the rivets are frequently brazed or soldered to prevent tank leaks. Ends can then be hemmed in and soldered, or flanged and brazed (and/or sealed with an epoxy-type sealant) or the ends can be flanged and then welded. Once the soldering, brazing or welding is complete, the fuel tank is leak-tested. In the aerospace industry, the use of Fuel Tank Sealants is a common application for high temperature integral fuel tanks. This provides excellent resistance to fluids such as water, alcohols, synthetic oils and petroleum-based hydraulic fluids. Automotive fuel tanks Passenger vehicles A larger fuel-tank results in a greater range for the car between refills, however the weight and space requirements of a larger tank are undesirable, especially in smaller cars. The average fuel tank capacity for cars is . The most common materials for fuel tanks are metal or plastic. Metal (steel or aluminium) fuel tanks are usually built by welding stamped sheetmetal parts together. Plastic fuel tanks usually built using blow molding, which allows more complex shapes to be used. Some vehicles include a smaller reserve tank to be used when the main fuel tank is empty. Some other vehicles, typically 4WD vehicles, have a large secondary tank (or "sub-tank") to increase the range of the vehicle. Racing fuel cell A racing fuel cell has a rigid outer shell and flexible inner lining to minimize the potential for punctures in the event of a collision or other mishap resulting in serious damage to the vehicle. It is filled with an open-cell foam core to prevent explosion of vapor in the empty portion of the tank and to minimize sloshing of fuel during competition that may unbalance the vehicle or cause inadequate fuel delivery to the motor (fuel starvation). Aircraft