This is a 4-step prop reamer for standard size prop shafts(American measures). This is NOT for metric shafts. It is used to enlarge the hole on the prop because most of the time the hole is too small to fit the engine. This is the best way to do it because it will not split the prop and will keep the hole perfectly centered. SPECS: It will ream holes with a diameter of 3/16", 1/4", 5/16", and 3/8". INCLUDES: One prop reamer WAJ 2/12/94 ir/jl