AirBlocks have a lightweight design and a unique patented bearing system which uses stainless steel balls in a captive, grooved race. Very high working loads in an extremely lightweight block, with the best strength-to-weight ratios around. Sheave: Delrin Sheave Size: 5/8" (16mm) Ball Bearings: Stainless Line Diameter: 7/32" max. Shackle/Strap Type: Loop top or swivel