These instrumented sheaves are used as fairleads and cable supports for various oceanographic instruments which require electrical conductor cable wire rope or synthetic rope. The snatch block configuration permits rapid placement and removal of the cable without removing the instruments or connector at the end of the cable. Aluminum and galvanized steel construction is used for light weight, strength, and resistance to corrosion. The Model 712 is available in several standard sizes. An electronic wire scope counter and a nylatron sheave are used in the instrumented models.