Pulley blocks are assemblies that consist of a hook or shackle, swivel, bearing, sheaves, sprockets, pins and frame. They are suspended by a hoisting rope or load chain and are designed for a variety of lifting applications. Pulley blocks often use eye hooks, clevis hooks, or grab hooks for connections to other lifting and rigging hardware. Pulley block shackles are U-shaped pieces of metal with a pin or bolt across the opening, or hinged metal loops that are secured with a quick-release locking mechanism. Pulley block swivels permit torsional rotation along one or more planes.
Many types of bearings are also used with lifting blocks. Pulley block sheaves are grooved wheels or pulleys that, when used with a rope or chain, change the direction and point of application of pulling force. Pulley block sprockets are designed to transmit power by means of a toothed wheel whose teeth engage the links of the chain.
Pulley block pins are of several different types. Choices include toggle, clevis, coiled, dowel, grooved, hinge, knurled, rolled, shear, spring, straight, taper or tension pins. The frames of lifting blocks are typically made of metal materials. Selecting pulley blocks requires an analysis of available product types and component specifications.
Most suppliers of pulley blocks designate products by application or feature. Choices include cargo blocks, deck blocks, crane block, pulley blocks, and bottom blocks. Parameters for lifting block shackles include pin or bolt diameter, hole diameter, width at eyes, width at bow, width between eyes, inside length, inside width at bow, outside diameter (OD) of eye, approximate weight, and estimated weight per hundred. Working load limit (WLL) is an important performance specification to consider.
Pulley block bearing parameters include bearing type, bore size, OD, and ratings from the American National Standards Institute (ANSI), Anti-Friction Bearing Manufacturers Association (AFBMA) and/or the Annual Bearing Engineers Committee (ABEC). Pulley block sheaves carry specifications such as sheave length and height, maximum cable OD, maximum sheave OD, minimum bending radius, maximum sheave width, shaft diameter, maximum line tension, and pulling radius. Important parameters to consider when searching for lifting block sprockets are number of teeth, bore diameter, hub diameter, OD, length through bore, and weight.