The term "pulley" and "block" can be interchanged. For wire from 3/32" to 5/32". These high load wire blocks are used for halyards, backstays, boom vangs and many other wire controls. The RF103 have flared cheeks to minimize chafing and removable sheaves for easy fitting and removal of the wire without cutting the termination. 1870 lbs maximum working load. 3740 lbs breaking load. 1-3/4" sheave diameter. 5/32" maximum wire.