A thread is the cheapest feature on a part and the first thing to fail. We machine external and internal threads to a defined class of fit, control the pilot diameter and face that set the joint, and inspect them before the parts ship.
Most thread problems are not thread problems. They are pilot diameter, face flatness, material or plating problems that show up at the joint.
A joint that loses preload vibrates, frets and then fails. Often the cause is a soft bearing face, a short thread engagement or no locking feature at all. We check engagement length and add nylon patch, threadlocking compound or a mechanical lock when the drawing allows it.
Stripping usually points to the wrong pilot hole, a coarse pitch in thin material, or aluminium threads loaded past their shear area. A change of pitch, an insert, or a switch to steel can add real margin. It costs less than scrapping assembled units.
Two good parts, one bad fit. Class of fit is the usual culprit. A 6g external thread and a 6H internal thread have defined limits, and plating adds thickness to both. We machine to the class called out and account for coating build-up.
Customers with go/no-go gauges reject parts we thought were fine. Thread form, lead and flank angle all show up at the gauge. We check with the same class of gauge before shipment so the parts pass at your dock, not just ours.
A thread only works when the pilot, the face and the material around it are correct.
Triangular threads carry the load in almost every fastener. Metric coarse, metric fine, UNC and UNF cover most work, and we cut all of them on the same machines. Trapezoidal and buttress forms appear on lead screws and jacks where the load runs one direction. Pipe threads need a seal, so the taper and the flank do the work, not the torque.
Class of fit decides whether the parts assemble by hand or by wrench. A 6H internal thread with a 6g external thread is the normal clearance pair. Where a coating is applied after machining, we leave room for the build-up or mask the thread. Plating a tight thread is one of the fastest ways to turn a good part into scrap.
A tightened bolt should carry the working load as tension, not as bending. Preload comes from torque, and torque depends on friction on the threads and under the head. A rough or plated surface changes that friction and the preload with it. We keep the bearing face flat and the surface finish consistent so the torque-to-preload relationship stays predictable.
Locking is a separate decision. A nylon patch, a prevailing torque nut, a serrated flange or a threadlocking compound each suit different service conditions. Where the joint sees heat or repeated disassembly, we avoid plastic-based locks. Where the joint is permanent, a chemical lock is often enough.
A short guide to the decisions we make with customers at the drawing stage.
| Situation | Thread choice | Locking method |
|---|---|---|
| General steel fastener | Metric coarse or UNC | Split washer or nylon patch |
| Thin aluminium wall | Fine pitch or insert | Prevailing torque nut |
| High vibration, serviceable | Metric fine | Serrated flange nut |
| Permanent joint | Metric coarse | Threadlocking compound |
| Fluid or gas seal | NPT or BSP taper | Sealant on the thread |
| Lead screw or jack | Trapezoidal or buttress | Nut with backlash control |
One shop for the thread, the pilot hole, the mating face and the finish.
Turned and thread-milled external threads on shafts, studs and fittings, with the pilot diameter and shoulder face cut in the same setup.
Tapped and thread-milled internal threads in aluminium, steel, stainless and titanium housings, from M2 up to large bores.
Multi-port blocks with several thread sizes, kept on a common datum so the ports line up after assembly.
Bolt hole patterns machined on a rotary table or 5-axis machine, with the pitch circle and hole positions held together.
Bosses sized for inserts, or holes prepared for heat-set and helical inserts in plastics and soft alloys.
One threaded prototype or a 10,000-part run, machined to the same drawing and the same class of fit.
Limits taken from our machine list, not from a catalogue.
| Item | Capability | Note |
|---|---|---|
| Tolerance | ±0.005 mm | On critical diameters and faces |
| Surface finish | Ra 0.8–1.6 μm | Ra 0.2–0.8 μm on request |
| Max part size | 4,000 mm | Long shafts and rails |
| Thread milling | 5-axis and mill-turn | Threads near shoulders and thin walls |
| Bolt circles | Ø400 mm rotary table | Indexed positions in one setup |
| Inspection | 100% before shipment | Gauge and optical checks |
Data first, adjectives last.
Fifteen years of cutting threads in aluminium, steel, stainless, titanium and plastics, on parts from one-off prototypes to long production runs.
Critical diameters and mating faces held to ±0.005 mm, so the pilot and the thread agree with each other after assembly.
Turning, milling, mill-turn and 5-axis capacity in three plants, which keeps the thread and the pilot in the same process.
Long threaded shafts, rails and tie rods that most shops cannot hold without repositioning.
A quotation and a free DFM review of your thread callouts within 12 hours of receiving the drawings.
Parts that pass inspection on the first submission, backed by raw material checks and in-process monitoring.
Light alloy brackets where every gram counts and the bolt circle must line up with the mating frame.
Housings and brackets that see vibration for years and cannot afford a loose fastener.
Stainless and titanium bodies with fine threads that must assemble cleanly after passivation.
Long threaded rails and tie rods where the thread runs several hundred millimetres from the datum.
Unless the drawing says otherwise, we cut a 6H internal thread and a 6g external thread. That is the standard clearance pair for general assembly.
If the joint is coated after machining, we adjust the limits or mask the thread so the finished part still assembles to the intended fit.
A common rule is one times the nominal diameter in steel and around two times in aluminium or plastics. That is a starting point, not a limit.
The real answer depends on the shear area of the weaker material. Send the load case and we will check the engagement against the material you have chosen.
Yes. Thread milling works well for large diameters, thin walls and threads close to a shoulder where a tap cannot reach or would break.
It also lets us correct the pitch diameter on a second pass, which a tap cannot do.
It will if nobody plans for it. Electroless nickel and zinc add thickness to both flanks and the crest, which tightens the fit.
We size the thread before coating or mask it, depending on the finish and the class of fit you need.
Match it to how often the joint opens and to the temperature. Nylon patches and chemical locks work for serviceable joints at moderate temperature.
For high temperature or repeated disassembly, use a prevailing torque nut or a mechanical lock instead.
We use go/no-go gauges of the same class called out on the drawing, plus optical checks on form and lead where the gauge alone is not enough.
Inspection is 100% before shipment, and reports are available on request.
Yes. Missing pitch, class or coating allowance is common on early drawings. We flag it in the DFM review.
The quotation and the free DFM analysis come back within 12 hours, so the question is usually resolved before you place the order.
No. We machine from one prototype to runs of 10,000 parts or more.
Uploads are kept secure and confidential, and an NDA is available on request.
We will review the joint, flag anything missing and quote it within 12 hours.
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