How wrenches are made

One forging can become more than one wrench size, because the jaws are cut to size afterward.

stations: 9
things upstream: 45
raw sources: 20
steps from the ground: 6

The short version

Most wrenches begin as rods of 6140 chrome vanadium steel. A hot billet is drop-forged to rough shape, then annealed soft so a broach can size the jaws and a press can stamp the markings. Only then is the wrench hardened, quenched in hot oil and tempered, before polishing and a nickel and chrome plate.

Cut and heat the billet

Long rods of 6140 chrome vanadium steel are cut to size and often sand-blasted clean. Each billet then goes into a furnace until it is hot enough to flow.

Goes in
Steel Chromium Vanadium
Drop-forge the shape

A drop hammer pounds the billet into closed dies, giving head and handle in one piece. The result is a rough forging with the right shape but not yet the right dimensions.
Trim the flash

A press punches away the flash that leaked out between the dies and opens the center of ring-shaped heads.
Soften by annealing

The cooled forgings are heated again and slowly brought down. This softens the steel enough to be cut and marked.
Broach the jaws

A broach, a bar whose teeth each stand slightly taller than the last, is pulled through the opening until it reaches the exact size for a bolt head.
Stamp the markings

A punch press drives in the size, the part number and the maker's name while the metal can still take it.
Harden and temper

The wrench is heated and quenched in hot oil, which slows the cooling and avoids micro cracks. A second gentler heating takes out the brittleness, and a tester checks the hardness.
Polish the surface

Machines or hands polish away the marks of forging. This is the first step that sets how the finished tool looks.
Plate in chrome

In an electroplating bath, a flash of nickel goes on first and a layer of chrome on top. Some wrenches get a black oxide finish instead.

Goes in
Nickel Chromium

End of the lineWrench

Worth repeating

In the United Kingdom, Ireland, Australia and New Zealand the same tool is called a spanner.
In North American English, a spanner is a specialized wrench with pins or tabs for round nuts.
Wrenches are often quenched in hot oil, because cooling the steel too fast can leave micro cracks in it.