With a sheave Ø of 29 mm (1 1/8 in) and a maximum line Ø of 8 mm (5/16 in), the Harken 29mm Double Block Swivel (Part No. 342) is designed to work seamlessly with the Big Boat blocks and features the Carbo Air line. Combining lightweight, durable materials with an affordable price, this small block has a maximum working load of 299 kg (660 lbs) and provides low-friction performance.