This is the Piston and Sleeve for the Traxxas 2.5 Revo Engine. FEATURES: Piston/sleeve is ABC construction. Four port design. INCLUDES: One piston One sleeve REQUIRES: Installation into 2.5 Revo engine. SPECS: Sleeve length: 27.6mm (1.08") Piston diameter: 14.7mm (0.58") COMMENTS: The sleeve has a notch for correct positioning.