Master composite low friction ball bearing blocks are engineered for competitive sailing. The high strength composite sideplates are to provide top performance of working loads. Beautiful design and simple use.↵Ball bearings: self-lubricant acetal composite↵Sheave diameter 40 mm: self-lubricant acetal composite↵Cheeks: reinforced glass fiber Nylon composite UV stablized↵Swivel shackle: Forged Grade 316 Stainless Steel↵WL: Working Load↵BL: Breaking Load↵NOTE: Working/breaking load of blocks with cam are based on the strength of the cam.