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. Features through-hub mounting for maximum strength. Requires 2 x 4mm fixing screws (not supplied).