Harken's 57mm Fiddle Block with a Swivel Part No. 2621 has a 57 mm sheave diameter (2 1/4 in), can handle lines up to 10 mm (3/8 in) in diameter, and has a maximum working load of 359 kg (792 lb). These low-friction Carbo Air blocks are not only lightweight and reliable, but also have very high working loads, making them a perfect companion to Harken's Big Boat blocks. Keep your trimming safe and easy with these compact yet strong blocks.