Use 57 mm Black magic AirBlocks on offshore boats. These strong, lightweight blocks are of sculpted aluminum, with Torlon rollers and carbon black balls for strength and UV protection. Rollers are housed in a unique center cage and isolated for less friction. Blocks feature a three-way head system and come in high and low load configurations. 11/8 in LINE, SWL 1655#, BS 3310# WT. 5OZ SHEAVE 57mm.