Single block with aluminum cheeks and ball bearing sheave. Delrin(tm) ball bearing sheave ensures low-friction operation. Sheave Dia. 1 7/16, Thickness 3/4 (19mm), Width 1 9/16 (40mm), Length 3 25/32 (96mm), SWL 1000 lbs (410 kg), Weight 2.4oz. (68g), Max Line 7/16" (12mm)