G'Day Rich,
Right area just need a bit more of a clue as to what it is your after.
Do you want to know the size of the pulley to attach to your engine to drive a pump? Also it helps sometimes to have an image to view as sometimes descriptions are different to what is being asked for.
Is there a name on the pump, size of pump etc? these also help with getting you the right reply.
Welcome to the Forum.