Thread grinding gets grouped together as one process, but external and internal thread grinding place very different demands on a machine, and the right choice depends on the part in front of you.

External thread grinding covers the more familiar case: precision fasteners, lead screws, and worm gears where the thread sits on the outside diameter. Because the grinding wheel approaches an accessible surface, external thread grinding generally supports larger diameters and longer thread lengths in a single setup — Veltrix's TP-715 and TP-760 cover component diameters from roughly 5 mm to 300 mm depending on configuration.

Internal thread grinding is the harder problem: the wheel has to reach inside a bore, which limits wheel diameter, reduces rigidity, and generally demands tighter process control to hold the same tolerance an external thread would need. It's the process behind precision nuts, internally threaded housings, and hydraulic and aerospace components where the thread has to be inside the part, not on it.

In practice, the part geometry decides the process — there's rarely a genuine choice between the two for a given feature. The real decision point for a shop is whether its thread grinding equipment covers both cases, or whether internal work is being sent to a subcontractor. A machine line built to handle external and internal thread grinding as core, equally-supported capabilities — rather than internal as an afterthought — is what keeps that work in-house.