This is a replacement Starting Pin and Pressure Spring for the HPI Nitro Star T-15 pull start engine (HPIG5101). These parts are installed into the back of the crankshaft and is what the starting shaft keys into to engauge the recoil. Steel construction One steel starting pin One steel spring Installing into the engine following the engine's manual Pin Spring Length: .167" (4.25mm) .248" (6.3mm) Diameter: .110" (2.81mm) .101" (2.5mm) kpm01/20/2004 ir/jxs &