A block chain, also called a "bar-link" or "block-and-bar" chain, is a mechanical drive chain

Chain

A chain is a sequence of connected links.Chain may also refer to:Chain may refer to:* Necklace - a jewelry which is worn around the neck* Mail , a type of armor made of interlocking chain links...

. It is composed of side plates, where each plate straddles one end of a block and is connected to the block with a pin going through a hole at one end of the block. Block chain is simple, but compared to modern roller chain

Roller chain

Roller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power on many kinds of domestic, industrial and agricultural machinery, including conveyors, wire and tube drawing machines, printing presses, cars, motorcycles, and simple machines like...

is heavy and is less efficient rolling over sprockets due to the lack of rolling motion as the chain engages and disengages the sprockets. However, it has advantages in specific applications and while not dimensionally standard like roller chain, it is commonly used for specific applications, especially where no sprockets are needed, loads are very high and strength is greater concern than efficiency, and where the chain has special fixtures for holding or engaging a load