#of sheaves

Hello! Going to be replacing my spin halyard sheaves, and i can't remember if there are one or 2 that are used for it. The mast is up and I wanted to order parts to be ready for season's end. I know of the 1" one that is on the outside of the mast where it exits, but is there another one behind it in the mast so as to not interfere with the jib halyard?