Barton Size 4 58mm Plain Bearing Pulley Upright Block [N04150] Transistor Student version 2019.pdf First transistor: Original. Size 4 58mm Plain Bearing Pulley Upright Block The Size 4 Barton range of blocks has a 58mm (2 5 16) sheave. They are of a rugged construction featuring high grade molded 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 compatible with our ball bearing mainsheet traveler system. The 54mm sheave Size 4 range is of rugged construction, featuring high grade molded 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 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 compatible with our ball bearing mainsheet traveller system. Suitable for up 12mm (7 16) rope. Quick Guide (pdf)