Losing air from a motorcycle tire can have grave consequences. Manufacturers themselves state that an uncapped tire stem is not secure from leakage without a sealed cap. These practical and well-made valve caps seat an 0-ring to provide that final seal, and have flexible retainers that ensure you won’t misplace them. Neat. Nylon version are fully compatible with the latest Tire Pressure Monitoring (TPM) valves made from aluminum. Brass (set of 4). Nylon (set of 5).