The Effects of Torque on Bolts

• The proper amount of torque holds a bolt in place without damaging it. garysludden/Photodisc/Getty Images

  Metal is a sturdy but pliable material used in almost all parts of a vehicle. Some metal joints are held together with welds, such as frames or body panels. Other elements of a vehicle are held using bolts. You secure bolts by applying torque, or force, creating a certain amount of pressure, which can have an adverse affect on the metal bolts.

Sheering

• Excessive torque can sheer off a bolt. The pressure created by the torque weakens the bolt, allowing it to fracture on existing fault lines within the structure. Forged metal has air pockets and microscopic cracks that take away from the metal's integrity. Engineers determine at what level of torque a metal will sheer and typically label that as the maximum torque for the bolt.

Stripping and Rounding

• Nuts or housings use threads that correspond with the threads on the bolts. Proper torque places sufficient pressure on the threads to lock them in place. Excessive torque bends and damages the threads, stripping the bolt or the housing. The heads may also be stripped when the bolt has reached the maximum torque, by rounding off the soft metal of the head. Rounding, as it is called, renders a bolt virtually useless.

Heat

• Force is a measure of speed and weight. Use of high-speed tools, such as air guns, increase the level of torque applied to bolts. Higher speeds and higher pressure translate to higher heat, which can cause a bolt to fuse to the nut or housing. Excessive torque also impacts the bolt's ability to stretch and spread when naturally heated from use. Too much pressure may cause the housing or nut to crack when the bolt heats up. Insufficient torque can cause the bolt to become loose and fall out in colder climates.