Fast Eddy, engine rotation socket. 24-splineUsed to rotate the engine from the sprocket shaft (with 24 splines); when doing engine building; timing; pushrod or other adjustment checks for which the engine must be rotated. The spline fit has intentionally been made with just a hair of extra play so the socket slides onto your sprocket shaft with ease; even if it''s an old shaft that has a couple burs or defects in it. Made from heat threaded 4140 steel. Cerakote finish.