A traveling block is the freely moving section of a block and tackle

Block and tackle

A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks so that one is fixed and one moves with the load...

 that contains a set of pulleys or sheave

Sheave

A sheave is a wheel or roller with a groove along its edge for holding a belt, rope or cable. When hung between two supports and equipped with a belt, rope or cable, one or more sheaves make up a pulley. The words sheave and pulley are sometimes used interchangeably.A sheave can also refer to a...

s through which the drill line

Drill line

In a drilling rig, the drill line is a multi-thread, twisted wire rope that is threaded or through the traveling block and crown block to facilitate the lowering and lifting of the drill string into and out of the wellbore....

 (wire rope) is threaded or reeved and is opposite (and under) the crown block

Crown block

A crown block is the stationary section of a block and tackle that contains a set of pulleys or sheaves through which the drill line is threaded or and is opposite and above the traveling block....

 (the stationary section).

The combination of the traveling block, crown block

Crown block

A crown block is the stationary section of a block and tackle that contains a set of pulleys or sheaves through which the drill line is threaded or and is opposite and above the traveling block....

 and wire rope drill line

Drill line

In a drilling rig, the drill line is a multi-thread, twisted wire rope that is threaded or through the traveling block and crown block to facilitate the lowering and lifting of the drill string into and out of the wellbore....

 gives the ability to lift weights in the hundreds of thousands of pounds. On larger drilling rigs

Drilling rig (petroleum)

This article lists the main components of a petroleum onshore drilling rig.Offshore drilling rigs have similar elements, but are configured with a number of different drilling systems to suit drilling in the marine environment....

, when raising and lowering the derrick, line tensions over a million pounds are not unusual.