Stand Up Spring Block. Machined anodized aluminum cheeks with 316 Stainless Steel spring and base. Anodized aluminum sheave runs on Torlon(tm) rollers and Delrin(tm) ball bearings for a low-friction strong block. Order backing plate 97-36 sold separately. Safe Working Load 2800 lbs (1270kg), Weight 10.4oz (295gm), Max. Line 1/2" (12mm), Sheave Diameter 2.6" (66mm), Base 2 3/8" Diameter (60mm). Requires (4) 1/4" (6mm) Flat Head Fasteners.