Hardware Part 1: Nuts, Bolts, Fasteners

We’ve talked about some advanced stuff in our tech series…shock valving, suspension frequencies, aerodynamics, and so on. But if you want to work on your car and actually get at some of the components we’ve discussed, we’ve got to talk about nuts and bolts.

Yeah, seems simple. But take several steps back with us in this article as we talk about some hardware basics. Nuts, bolts, fasteners…the stuff that can turn a quick install into a nightmare or a fun track day into a disaster.

First up: we’re going to stick with the metric system since that’s what we almost always use on our cars.

We also won’t get into materials here, but there are pros and cons to different types of steel, aluminum, titanium, as well as the various finishes, coatings, and hardware grades out there. We’ll talk about that another time.

There are different head types, too, like stars, allens, squares, but usually we’re using good old hexagonal heads.

A metric bolt is described by the diameter, thread pitch, and length.

Example:

M12 x 1.75 – 20 millimeter (mm) length

That’s a bolt where the diameter of the thread is 12mm, the thread pitch is 1.75, and the length of the thread is 20mm.

Thread pitch is the distance in mm between threads. Importantly, not all M12 bolts use the same pitch. Getting this wrong will ruin your day (and not fasten anything correctly).

A thread checker like this can save you from a bad time.

You don’t want to force an M12x1.25 nut onto an M12x1.75 bolt.

A regular hex-head M12 bolt will usually require a 17mm to 19mm wrench or socket to tighten. You’ll be threading these into a nut or a tapped hole somewhere with matching thread pitch.

Nuts are also described by diameter and thread pitch. The diameter here references the bolt that they fit onto. An M12 hex nut will usually require a 17mm to 19mm wrench or socket.

You may also need to use a washer or a flange nut, which is essentially a nut with a built-in washer.

So you’ve got a bolt, a nut, the thread pitches match…time to crank that sucker down as hard as you can, right?

Let me tell you about “torque specs.” Torque is a force (how hard you’re pushing on the wrench) multiplied by a distance (the length of the wrench). The units we’re dealing with are either foot-pounds (ft-lbs) or Newton-meters (N-m).

A torque spec will tell you just how tight to tighten that nut or bolt. A torque wrench can be set to “click” and give a little when it reaches the desired torque.

Cheap torque wrenches aren’t very precise, and abused torque wrenches will be inaccurate. Don’t use them as a breaker bar to loosen a stuck bolt and don’t throw them around.

Final tightening of fasteners should be done with a torque wrench. Under-tightening is obviously bad as you want to avoid fasteners coming loose. But over-tightening can strip the threads on the fastener, deform parts, or simply break nuts and bolts. Over-torqued fasteners can also be difficult to remove, which is a problem for things like wheel nuts. Don’t try to guess the torque from an electric impact gun.

There’s much more to come in this series. Understanding hardware is a valuable skill for all enthusiasts.