What Is a Block Sheave Size?

The larger a block sheave's size, the more it aids in reducing work.

Sheaves and blocks are two parts of a pulley used to reduce the total amount of work that needs to be exerted. The two measures of these parts affect each other so their measurements are often listed together as one figure when referring to the block sheave size.

Definition

The term "block sheave size" refers to a compiled list of the two sizes of standard parts of a pulley: The block and the sheave.

Uses

Block sheaves are used in a pulley to divide a rope into multiple segments in order to shorten it. Doing so reduces the total amount of force needed to lift or move an object.

Determining Size

Block sheave size is determined by the weight of the object being moved and the length, width and material of the rope used in the pulley system.

Example

A standard block sheave size may appear as: 4", 1. In this case 4" refers to the diameter of the sheave, and 1 describes the number of blocks. They are often listed along with figures such as the diameter or the rope and the weight of the total load to be lifted since these figures also affect the block and sheave size.

References

• Block and Tackle Systems: Basics
• Gunne Bojohnson: Sheave Size
• Certex: Blocks and Sheaves