Barton Marine Size 3 45mm Plain Bearing Pulley Block Double w/Swivel [N03230]Size 3 45mm Plain Bearing Pulley Block Double with Swivel The size 3 Barton plain bearing blocks have a 45mm (1 3 4" sheave size 3 block range that incorporates modern design with stainless steel frames and the latest advanced materials, using 30% fiberglass filled nylon and Acetal sheaves to maximize their strength while keeping weight to a minimum. Suitable for use as mainsheet, vangs, lead blocks, or wherever a powerful and compact purchase system