30mm Cheek Block. Technical features of the BBB30: 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: 30mm Safe Working Load: 440lbs. Breaking Load: 881lbs. Max Line: 8mm. Bolt Size: 4mm.