Ronstan's Series 20 Ball Bearing Utility Blocks are a range of lightweight blocks with high static and dynamic load capacities and versatile head fittings. They feature precision-moulded, UV-stabilised acetal sheaves running on stainless steel ball bearings to give high performance and low friction. They are ideal for Dinghy control lines and vangs, cunninghams and traveller controls. Requires 2 x 4mm fixing screws (not supplied).