A
dustcap is a small
cover used on the
valve stem of a
bicycle or
car tire to prevent
dust or other small
particles from entering the valve and damaging it. The dustcap also forms a pressure seal, helping to prevent deflation of the
tire due to slight gas seepage past the tire valve. Dustcaps are usually made from
plastic but may occasionally be made of
metal. The dustcap is internally threaded and is secured by screwing it onto the end of the stem. To prevent corrosion due to
electrolysis and malfunction of the electronics in a
direct TPMS and avoid costly repairs, metal valve caps without insulating plastic linings should not be used on direct-TPMS-equipped tire valve stems.