The Torque Wrench Is a Fascinating Piece of Engineering

If you work on cars, you probably own a torque wrench. Responsible for tightening nuts and bolts down to precise measurements, they’re used mostly for assembling things like engines, where fasteners have to be tightened with a specific amount of force to function properly. How a torque wrench works is surprisingly straightforward, but fascinating nonetheless.

The Deconstructed YouTube channel published a video detailing the inner workings of an average ratcheting click-type torque wrench—the type you’re probably used to, where adjustments are made via the lines on the handle. Unlike some more ultra-fancy digital torque wrenches, this thing is totally analog, with no sort of battery power. 

This type of torque wrench starts off normally enough, with a standard ratcheting socket attachment point at the top. That ratcheting piece is attached to the wrench body via a single, centrally located pin near the top of the wrench body, allowing it to pivot on its axis within the wrench cylinder. A spring at the bottom of the torque wrench tensions that ratchet against a small metal cube called a pivot block. Using a set of slots between the spring and the ratchet piece, that block will eventually shift within its mounting point when enough force is put on the ratchet. It’s that shift that causes the audible “click” you hear.

When that block shifts depends on the tension of the spring. And that tension is decided when you adjust the torque wrench using the handle. The more tension in the spring, the more force it’ll take to get that pivot block to shift. 

That tension is also why it’s important to store your torque wrench on the lowest setting. This relieves the spring of all that pressure, which, if left unchecked, could cause “creep,” or a slow deformation of the spring. That would throw your wrench’s calibration out of whack, and no one wants that.