Ideal for high load applications. Wear resistant sheave material, in lightweight, self lubricating polymer, is suitable for use with rope or wire.Captive Lock™ universal head can be fixed in either of two planes, or free to swivel as required. Block pulley, used for dredges and rigging outriggers. Single Block, swivel head with shackel. All with ball bearings. Fits up to 1/4" - 3/8" line.