The Size 4/5 Barton range of blocks have a 54mm/ 2 1/8Ó sheave. These Ball Bearing blocks are a rugged construction, featuring high grade moulded side plates that are through-bolted and riveted for added strength and security. All load carrying components and interior frame are from marine grade 316 stainless steel and are also available in plain ball bearing sheaves are available. This sleek and versatile range is engineered for use on larger cruising and racing yachts and is compatible with our ball bearing mainsheet traveller system. Suitable for up 12mm Ð _Ó rope.