Most types of spanner are made using the drop forging process.
Steel rods are cut into short lengths, called billets, and each one is passed through an induction heating coil which uses electromagnetism to heat the metal to about 1000 degrees Celsius.
The billet is placed in three dies (also known as ‘moulds’) in succession. The upper die drops onto the billet, forcing it into shape. The first die provides the rough shape of the spanner, the second the finished shape and the third trims the excess metal from the formed spanner.
The ‘trim line’ (the place where the two halves of the die come together) is ground down to produce a smooth surface and a hydraulic press stamps the manufacturer’s name and the product details into the spanner’s surface.
If the spanner has an angled head, a machine bends the end of the spanner into shape.
If the spanner has a ring or flare nut head, a vertical milling machine cuts a hole through the centre of the head ready for shaping and sizing with a broach machine.
Box and spark plug spanners are not made by drop forging. They are made from steel tubing that is shaped with forming tools which push into the ends of the tube, creating the profiles.
The spanners are then tempered to increase the steel’s strength. Tempering is a specific sequence of heating and cooling which is slightly different for each type of steel.
Flare nut heads are created after tempering by cutting a small section out of the front of the head.
The spanners are left in a constantly moving tub of ceramic stones and chemicals for half a day to prepare the surface of the tools for coating.
Some spanners are electroplated by being dipped in a sequence of baths containing nickel and chromium solutions. Electricity passing through the spanner causes particles of metal to stick to the tool, creating a very thin layer of metal on the surface.
Others are coated with black oxide by being immersed in a chemical solution which reacts with the iron in the steel, producing a covering of magnetite which protects the steel from corrosion.
Spanners are also dipped in a rust inhibitor solution for extra corrosion protection.
If the spanner has multiple components, they are fitted together, often by hand. For example, rivets are fitted to hold the heads of flex-head spanners in place and plastic gears, made using injection moulding, are fitted into the heads of ratchet spanners.
Injection-moulded components are made in a mould into which molten plastic is pushed under pressure. Once the piece is set it can be removed and ground down to smooth it into the finished component.
Fully insulated spanners are made by placing the spanner in an injection mould and injecting molten plastic into a cavity surrounding the tool so the spanner emerges with a plastic coating.
Finally, each tool is tested to ensure it is strong enough to meet the manufacturer’s standards.