40mm Single Block with Shackle Swivel. Technical features of the BBB40: Stainless steel ball bearing races, stainless steel ball bearings and glass fibre reinforced sheave for best strength even under high dynamic loads. Acetal bearing cage to prevent ball-to-ball friction and to reduce weight. Composite, 50% Glass fibre and 50% Polyamide. Sheave diameter: 40mm. Safe Working Load: 551lbs. Breaking Load: 1102 lbs. Max Line: 10mm. Bolt Size: 4mm.