Greenlee 651 Hook Sheave, 4000-Pound Capacity, 12-Inch Strong, welded steel frames Forged steel closure-type hooks with 1-Inch (25.4 mm) opening 5-Inch (127 mm) wide aluminum alloy sheaves with self-lubricating bearings 4000-Pound maximum pulling capacity Outside diameter 12-Inch, inside radius 3-5/16-Inch