Also the actual shap of the groove in the sheeve is different between the older sheeves that accepted wire rope only. I replaced my wire rope halyard with a high-tech synthetic rope. At the same time, I replaced the old metal sheeves with delrin sheeves designed to accept either wire or synthetic rope. If in doubt, I would contact Hall Spars and
Rigging. Nan Hall was extremely helpful and ensuresd I had exactly the right parts for my boat.