Cold Heading vs Machining: How Custom Bolts Are Made, and How to Choose

Most custom bolts are made one of two ways: the head and shape are cold-formed from a coil of wire, or the part is machined — cut from bar stock on lathes and machining centres. Both routes produce bolts that can look identical in a photograph and meet the same drawing. They differ in what shapes they do well, how cost behaves with quantity, and which one should make your part.

We run both lines: cold heading for M5–M24 and machining for custom bolts in M8–M64. That overlap — M8 to M24, where either process could make the part — is where the interesting decision lives, and it is the subject of this guide.

What cold heading does

Cold heading starts with a coil of steel wire. A length is cut, then a series of dies strikes the blank at room temperature, progressively forming the head and shank shape; threads are typically rolled afterwards. The metal is displaced, not removed.

Because the grain of the steel flows with the shape rather than being cut across, cold-headed parts are strong for their size, and because almost no material becomes scrap, the process is economical at volume. Its limits are geometric: shapes must be formable by dies in sequence, very large diameters exceed machine capacity, and each new shape needs its own tooling.

What machining does

Machining starts from bar stock and removes material: turning the shank and steps on a lathe, milling flats or special profiles, drilling cross-holes, cutting or rolling the thread. Almost any geometry that can be drawn can be machined, including large diameters — our machined custom bolts run to M64 — and asymmetric or intricate features that no die could form.

The cost structure is the reverse of heading: tooling is light, but every part consumes machine time and a share of the bar becomes chips. At low quantities or high complexity, that trade is worth it. At high quantities of a formable shape, it usually is not.

The overlap: M8–M24, decided by four factors

When a part falls in the overlap range, the decision is made on these factors, in roughly this order:

Two qualifications matter here. First, quantity interacts with tooling: when a new shape needs heading dies and there is no existing sample or tooling, a mold fee applies — quoted separately, as described in our custom bolt quote checklist. A modest first order can still favour heading if repeat orders are expected, because the tooling is paid once. Second, the final call is made in technical review, from the drawing: some shapes that look formable are not, and some that look complex head surprisingly well. The table is a planning guide, not a verdict.

What about tolerances?

Both processes hold our general tolerance of ±0.05 mm on the dimensions that matter. Machining is the more flexible route when a single feature needs a tighter or specifically controlled dimension, because that feature can be finished individually; heading holds its dimensions through the dies, which is consistent across a long run once tooling is proven. If your drawing carries a tolerance tighter than ±0.05 mm on a critical feature, flag it in the inquiry — it can influence which process the review recommends.

Strength is set by class, not by process

Buyers sometimes assume a machined bolt is “stronger” or a headed bolt is “cheaper quality.” Neither is a property of the process. Strength comes from the material and heat treatment that deliver the specified property class — 4.8, 8.8, 10.9 or 12.9 — and both of our lines produce to the class on the drawing, verified by the same in-house testing (composition, hardness, metallography, dimensions). Choose the process for geometry and quantity; choose the class for load.

Common mistakes

• Insisting on machining for a simple, high-volume shape. You pay machine time for what dies would form in a fraction of the time, on every single piece.
• Insisting on heading for a shape with cross-holes or milled features. Those features need machining operations anyway; the review will say so, later than it should have been raised.
• Comparing only the first-order price. Tooling is a one-time cost; unit price repeats forever. Compare across the expected life of the part.
• Not mentioning expected repeat orders. As with tooling generally, expected volume changes the recommendation — say it in the first message.

FAQ

Can the same bolt be quoted both ways?
In the overlap range, yes — the technical review can price the part as headed and as machined when the geometry allows both, so you can see the tooling-versus-unit-price trade with real numbers.

Is there a size where machining is the only option?
Above M24, yes for our production: cold heading covers M5–M24, and larger custom bolts are machined. Below that, complexity can make machining the right answer at any size.

Does cold heading need a sample?
A sample or an existing specification speeds up tooling decisions. Without one, new tooling may be required and a mold fee applies, quoted as its own line.

Which process should I ask for in my inquiry?
You do not need to choose. Send the drawing, quantity, and property class via the custom fasteners page; the review recommends the process and explains why with the quotation.

HyHaven manufactures custom fasteners by cold heading (M5–M24) and machining (M8–M64), to your drawing or sample, from 2,000 pieces. Request a quote.