Threading is the operation that creates a thread, that is, a helical groove, on a cylindrical or conical part so that it can be assembled by screwing. We distinguish external threading, on a rod (screw, stud, pin), from internal threading, done in a hole by tapping. The word also refers to the thread itself.
Several processes coexist. On a lathe, a profiled threading tool removes material in several passes synchronised with the rotation. In milling, a thread mill describes a helix around the hole or the rod. Thread rolling forms the thread cold, by pressing the part between rollers: it is very productive for high-volume screws and improves fatigue strength because the metal fibres are not cut. The die is used for small runs, and thread grinding for hardened parts and precision screws. The most common systems are ISO metric (M), coarse or fine pitch, inch threads (UNC, UNF), pipe threads (G, R, NPT) for fluid fittings and trapezoidal (Tr) for lead screws.
Threads are cut on special screws, pins, cylinder rods, end fittings, connectors and bushes. For ordinary fixings, it is better to choose a standard thread: tooling and gauges exist everywhere, which eases sourcing and inspection. Threading is part of the CNC machining and mechanical engineering and assembly capabilities.
In a quote request. Give the full designation (for example M12 × 1.5 – 6g), the threaded length, the thread direction (right-hand by default) and the thread run-out. If a treatment such as zinc plating is planned, say whether the tolerance applies before or after treatment: the thickness deposited can prevent a thread machined to nominal size from screwing in. The guide on the manufacturing specification helps you leave nothing out.