Impeller. Pump:F5. Material:MC97 (for cooling). Outer Diameter:2.25". Inner Diameter:Splines. Width:1.24". 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.