Fiddle block works with 25-53 for a strong 4:1 purchase. Delrin(tm) sheaves run on plain bearings for high static load strength. Sheave Dia. 1 1/16" (27mm), Thickness 15/32" (15mm), Width 1 7/8" (48mm), Length 4 7/16" (112mm), SWL 900 lbs, Weight 2.5 oz (71g), Max Line 5/16" (8mm)