Barton Marine 54mm Single Swivel Block Size 4The Size 4 Barton range of blocks have a 58mm (2 5 16) sheave. They are of a rugged construction featuring high grade moulded side plates that are through bolted and riveted for added strength and security. All load bearing components and interior frame are from marine grade 316 stainless steel and both plain and ball bearing sheaves are available. This sleek and versatile range is engineered for use on larger cruising and racing yachts and is