TACKLE TERMS

To help avoid confusion in working with tackle, you need a working knowledge of tackle vocabulary. Figure 4-20 will help you organize the various terms.

A fall is a line, either a fiber line or a wire rope, reeved through a pair of blocks to form a tackle. The hauling part is the part of the fall leading from one of the blocks upon which the power is exerted. The standing part is the end of the fall, which is attached to one of the beckets. The movable (or running) block of a tackle is the block attached to the object to be moved. The fixed (or standing) block is the block attached to a fixed objector support. When a tackle is being used, the movable block moves, and the fixed

Figure 4-20.-Parts of a tackle.

block remains stationary. The term "two-blocked" means that both blocks of a tackle are as close together as they will go. You may also hear this term called block-and-block. To overhaul is to lengthen a tackle by pulling the two blocks apart. To round in means to bring the blocks of a tackle toward each other, usually without a load on the tackle (opposite of overhaul).

Don't be surprised if your coworkers use a number of different terms for a tackle. For example, line-and-blocks, purchase, and block-and-falls are typical of other names frequently used for tackle.

BLOCK NOMENCLATURE

The block (or blocks) in a tackle assembly changes (or change) the direction of pull or mechanical advantage, or both. The name and location of the key parts of a fiber line block are shown in figure 4-18.

The frame (or shell), made of wood or metal, houses the sheaves. The sheave is a round, grooved wheel over which the line runs. Ordinarily, blocks used in your work will have one, two, three, or four sheaves. Blocks come with more than this number of sheaves; some come with 11 sheaves. The cheeks are the solid sides of the frame, or shell. The pin is a metal axle that the sheave turns on. It runs from cheek to cheek through the middle of the sheave. The becket is a metal loop formed at one or both ends of a block; the standing part of the line is fastened to this part. The straps hold the block together and support the pin on which the sheaves rotate. The swallow is the opening in the block through which the line passes. The breech is the part of the block opposite the swallow.

CONSTRUCTION OF BLOCKS

Blocks are constructed for use with fiber line or wire row. Wire rope blocks are heavily constructed and have a large sheave with a deep groove. Fiber line blocks are generally not as heavily constructed as wire rope blocks and have smaller sheaves with shallower wide grooves. A large sheave is needed with wire rope to prevent sharp bending. Since fiber line is more flexible and pliable than wire rope, it does not require a sheave as large as the same size of wire rope.

Blocks fitted with one, two, three, or four sheaves are often referred to as single, double, triple, and quadruple blocks, respectively. Blocks are fitted with

a number of attachments, the number depending upon their use. Some of the most commonly used fittings are hooks, shackles, eyes, and rings. Figure 4-21 shows two metal frame, heavy-duty blocks. Block A is designed for manila line, and block B is for wire rope.

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