How To Make Nuts and Bolts

Let's Talk Rusty Iron: Sam Moore discusses making nuts and bolts by hand, as blacksmith's did early in the machine age.

| September 2007

Anyone who works on rusty iron is familiar with nuts and bolts, as literally hundreds of these handy little gadgets are used to hold together the machines we all love. If we need a supply of new nuts and bolts, a quick trip to the local hardware store will usually suffice. But the fasteners weren't always so easy to obtain.

Early in the machine age, the necessary nuts and bolts were all handmade, with scarcely any two of the resulting fasteners being precisely the same shape, size or thread. In fact, the inventor of the forerunner of the modern Crescent wrench (a young Swedish machinery repairman named Johansson) grew so weary of lugging his large toolbox, heavy with all the different-size wrenches he needed, that during the 1880s he was inspired to invent the adjustable wrench.

One method used by blacksmiths to make a large bolt with a hex head was to take a length of iron rod the diameter of the desired bolt and cut it to length. A piece of square iron bar was heated and bent around a mandrel to form a ring with an inner diameter the same as the bolt size. This ring was placed over one end of the bolt and both were brought to a welding temperature in the forge and hammered until the ring was securely welded onto the rod end.

The new bolt head was then reheated and hammered into an angled notch in a swage block, turning the head again and again until the six sides were properly formed. This process usually left the top and bottom faces of the bolt head very rough, so another reheat and a different set of swages or a heading tool were used to flatten these surfaces. Final finishing was done with a file or a cupping tool.

Another way of making square- and hex-headed bolts was to heat and upset one end of a rod of the desired bolt diameter. Upsetting, or thickening (sometimes known as "jumping up") the end of a rod was accomplished by heating one end of the rod, holding the rod vertically on the anvil with the heated end up, and hammering on that heated end until it spread and thickened enough to provide sufficient metal to form the bolt head. The head was then reheated and the cold end of the bar was passed through a suitable hole in a swage block, or through a heading tool, where the upset end was hammered down against the block to form the flat underside of the head. The head was then made square by hammering and, finally, filing.

Small bolts were usually formed by using a case-hardened tool that had a round hole the size of the bolt shank but shorter than the length of the rod from which the bolt was to be made. Around the top of the hole was a depression the shape and size of the desired head, which could be hex or square. One end of a piece of iron rod was heated and the rod was placed in the hole with the heated end up. The smith then hammered the hot metal into the depression to form the bolt head.