A chain pulley block is the name for the portion of a block and tackle that the chain loops around. By itself, it really doesn’t do anything, but when combined with the entire system, it is part of a complex and useful device. By definition, a chain pulley block has more than one chain that loops through it and all the loops are connected to a single axle. Beyond that, the block can have a wide variety of shapes, sizes and configurations. When the chain pulley block doesn’t have any lines running through it, then it’s just a block, but when it’s strung onto a line, the whole system is called a tackle.
The essential construction of a chain pulley block is very simple. A single axle will have multiple rollers connected to it. It doesn’t matter how many rollers, as long as it is more than one. Other than that, the block can be made of any material, be of any size, and work with many or few other block. The appearance of the block and the rest of the system is unimportant.
Each roller in a chain pulley block is designed to have a single chain over it. Generally, these rollers have one of two appearances. Some appear as wheels with a concave groove along the edge that the chain sits in. The more common modern roller is a combined series of rollers that are all encased in a single protective cover. The cover usually has a spot where the line is fed into the block and then where it comes out; the rest of the block is covered.
The chain goes over the roller and out, over another roller in another block, then back to the first block and over the second roller. This turns the block into a system called a tackle, more commonly called a block and tackle. A tackle can contain more than one block or multiple two-block tackles can operate on the same line.
The purpose of a tackle is to create mechanical advantage. By running the line through the blocks, the operator creates a form of artificial leverage, much like using a lever and fulcrum to move a heavy object. Each time the chain is looped through the block, the system puts out more pulling power than what went in. When the user pulls the chain containing the tackle, the multiplicative effect will allow a single person to lift objects that weigh many hundreds of pounds with very little effort.