This is the Traxxas replacement piston and sleeve for the TRX Pro 15 engines.
ABC (Aluminum piston with a Brass sleeve or liner that is Chrome plated) ... Matched set with oil ring.
INCLUDES: 1 Piston ... 1 Ported Sleeve(liner).
There is a notch on the top of the sleeve (liner) to properly align with markings on the crankcase, to properly place ports ... The piston and sleeve is usually replaced after the engine performance weakens and compression is decreased after much use.