Impeller. Pump:F2. Material:Nitrile (oil resistant). Outer Diameter:1.29". Inner Diameter:0.31"/Flat. Width:0.50". A worn or damaged impeller can cause system failure or engine breakdown. SPX's Johnson Pump brand impellers are developed and manufactured for maximum flow and long life. With a genuine spare impeller you can also be sure that you are getting the quality required by engine manufacturers and professionals.