The size 3 Barton ball bearing blocks have 45mm (1Ó _) sheave size 3 block range incorporates modern design with stainless steel frames and the latest advanced materials, using 30% fibre glass filled nylon and Acetal sheaves to maximise their strength whilst keeping weight to a minimum. Suitable for use as mainsheet, vangs, lead blocks or wherever a powerful and compact purchase system is required on dinghies, dayboats and lightweight cruisers. Suitable for up to 10mm (3/8Ó) rope.