Final answer:
Using a length of pipe over the handle of a wrench helps provide additional leverage when removing a tight bolt. However, it can also be hazardous if excessive force is applied and the bolt breaks.
Step-by-step explanation:
When mechanics put a length of pipe over the handle of a wrench when trying to remove a very tight bolt, it helps by providing additional leverage. By increasing the length of the wrench handle, the mechanics are able to apply more torque to the bolt, making it easier to loosen. This is known as using a 'cheater bar' or 'pipe extension'.
However, using a pipe extension can be hazardous as it can put excessive force on the bolt and potentially break it. Mechanics need to be careful to apply only as much force as needed to avoid damaging the bolt or causing any other unintended consequences.