Lightweight 30mm blocks feature the same advanced materials and open design of Lewmar's 40mm blocks for high performance and reduced weight. The MRT (Metal Replacement Technology) sheaves, combined with the stainless steel central race and balls, deliver the ultimate efficiency and weight advantage. Cheeks use Long Fiber Technology giving exceptional strength and durability. Sheave: MRT Composite reinforced plastic Ball Bearings: Stainless steel central race and balls Cheek Material/Finish: Composite reinforced plastic Shackle/Strap Type: Stainless steel Ratchet: No