Half nuts worn out, and your lathe is not on anybody’s parts list? We machine replacement half nuts, split nuts and cross-slide feed nuts from your worn original — any make, any age, threads cut to match your leadscrew rather than a catalogue. One piece up, no drawing needed. Get a quote →
If you own a South Bend 9″, an Atlas 10″, or a Logan, you can buy half nuts or send yours for rebuild — a handful of specialists cover those models well. Everyone else runs into the same wall: Colchester, Harrison, Boxford, Myford, Monarch, Clausing, older European machines and the enormous population of imported lathes have no parts channel at all, and the advice on every forum ends the same way — make it yourself.
That advice is fine if you have a working lathe. It is circular if the machine you need to cut the part on is the one with worn half nuts. We work from your part and your leadscrew, not from a parts catalogue, so whether your lathe is listed anywhere makes no difference to us.
The question nobody answers: your leadscrew is worn too. A screw that has run for fifty years is worn most near the headstock and barely touched at the tailstock end. Cut a new nut to nominal ACME dimensions and it will mesh loosely exactly where you use the machine most. Any replacement that ignores this is half a repair — and it is the reason so many people fit new half nuts and still have backlash.
| Route | What we do | When it is right |
|---|---|---|
| Cut to the screw as it is | Thread the nut to the leadscrew’s actual measured size in its working section | Best fit today; the sensible default on a machine you are not rebuilding further |
| Compromise fit | Thread between the worn and unworn dimensions | Most common choice — usable along the whole screw, tightest where it matters |
| Matched pair | New leadscrew and new nut cut together as a set | The only route that restores original accuracy; worth it on a good machine |
Send a length of the screw, or measure it near the chuck and near the tailstock and send both numbers. We will tell you which route your machine actually needs — including when the honest answer is that your existing nuts are fine and the backlash is coming from somewhere else.
This is argued about endlessly and usually decided badly. The right material depends on what the original was, how hard the screw is, and how well the machine is actually lubricated.
| Material | Best for | Watch out for |
|---|---|---|
| Cast iron | The OEM norm on quality machines; excellent against an unhardened steel screw, graphite holds oil | Not the choice for shock loads; needs the original section to stay strong |
| Bronze SAE 660 | Machines cleanly, forgiving, good where lubrication is regular | Where oiling is intermittent it can wear the screw faster than cast iron — it is not a free upgrade |
| Brass C360 | The sensible replacement for Zamak pot-metal nuts on hobby machines — far harder than Zamak, still softer than the screw | Lower load capacity than bronze; not for heavy industrial feed |
| Acetal / Delrin | Light-duty and hobby machines; quiet, self-lubricating, sacrificial by design | Creeps under sustained high load; not for a production lathe |
| Steel | Where the original was steel and loads are high | Hardest on the screw — only when the original specified it |
Aluminium alloys such as 6061 or 7075 are not used for feed nuts — they gall against a steel screw. 304 or 316 stainless appears only on food and pharmaceutical machinery where washdown demands it. We recommend from your machine and its lubrication, not from whatever cuts easiest.
A half nut is not two nuts. The pair is bored and threaded as a single assembly and then split, so the thread is continuous and closes true on the screw axis when the lever engages. Halves threaded separately never close concentrically, and the result chews the leadscrew — converting a cheap repair into an expensive one. We cut the split face, keys and dovetails to your apron so the engagement is square, not cocked.
| Form | Where it turns up |
|---|---|
| ACME 29° | The classic American machine-tool leadscrew form (ANSI/ASME B1.5) |
| ISO trapezoidal 30° (Tr) | European and most modern metric machines |
| Whitworth 55° & BSW | Older British lathes — see also Whitworth & BSF fasteners |
| Square & modified square | Antique and heavy machinery power threads |
| Odd & obsolete pitches | Single-point cut, so no tap or die needs to exist |
Even stripped bare, the body outline, mounting holes, dovetails and split face are all still measurable. Broken in pieces is fine; send all of them.
Best: send a length of screw. Otherwise measure the major diameter near the chuck and near the tailstock, and count TPI or measure the pitch. This is what decides the fit. How we work from a sample →
Useful but not required. If your lathe has no badge, no manual and no parts list, we still make the part — that is the whole point.
Before you order, check it really is the nuts. Backlash you can feel at the handwheel is often the cross-slide nut rather than the half nuts, and sometimes it is a worn thrust bearing or a loose handwheel key that costs nothing to fix. Tell us where the play is and how it behaves at each end of the screw — we would rather tell you it is not the nuts than sell you a part that changes nothing.
My leadscrew is worn. Will a new half nut cut to the original spec actually fit?
Often not well, and this is the question almost nobody answers. A leadscrew that has run for decades is worn most in the section nearest the headstock and barely worn at the far end, so a nut cut to nominal ACME dimensions meshes loosely where you use the machine most. We offer three routes: cut the nut to the leadscrew as it actually measures today, which gives the best fit now; cut to a compromise between the worn and unworn sections, which is the usual choice; or replace the screw and nut together as a matched pair, which is the only route that restores original accuracy. Send a length of the screw or its measurements at both ends and we will tell you which one your machine needs.
Which lathes can you make half nuts for?
Any lathe, including the ones nobody stocks parts for. South Bend, Atlas, Craftsman and Logan are well served by existing sellers, but Colchester, Harrison, Boxford, Myford, Monarch, Clausing, older European machines and imported lathes with no parts channel at all are exactly the cases we take. We work from your worn nut and the leadscrew rather than from a parts catalogue, so whether the machine is listed anywhere is irrelevant.
What material should replacement half nuts be made from?
It depends on what the original was and how the machine is lubricated. Cast iron is the OEM norm on quality machines and remains an excellent bearing material against an unhardened steel screw. Bronze such as SAE 660 machines cleanly and is forgiving, but where lubrication is intermittent it can wear the screw faster than cast iron would, so it is not automatically the upgrade people assume. Brass 360 is the sensible replacement for the Zamak pot-metal nuts fitted to some hobby lathes, being much harder than Zamak yet still softer than the screw. Delrin and acetal work for light-duty machines. Aluminium alloys such as 6061 or 7075 are not used for feed nuts. We will recommend from your machine and its lubrication, not from what is easiest to cut.
Can you copy a half nut that is worn out or broken?
Yes, that is the normal job. A worn nut still carries every dimension that matters except the thread flanks: the body outline, dovetail or key features, mounting holes, the split face and the actuating geometry. We take the thread specification from your leadscrew rather than from the worn nut. If your nut is broken in pieces send all of them; if it is missing entirely, send photos and the leadscrew measurements plus the apron pocket dimensions.
Do the two halves close concentrically?
They must, and this is where a poorly made half nut fails. The pair is machined and threaded as one assembly and then split, so the thread is continuous and true across both halves when engaged. A nut whose halves were threaded separately never closes on the screw axis and chews the leadscrew. We also cut the split face and any keys or dovetails to your apron so engagement is square rather than cocked.
Which thread forms can you cut?
ACME 29 degree, ISO trapezoidal 30 degree, Whitworth and Acme-stub forms, plus square and modified-square power threads, in imperial TPI or metric pitch, right or left hand, single or multi-start. Threads are single-point cut on the lathe, so an obsolete pitch that no tap exists for is not an obstacle. That is the same capability behind our custom lead screws, which is why we can cut a nut and a screw as a matched pair.
Can you supply cross-slide and compound nuts too?
Yes, and most customers order them together because they wear together. Cross-slide and compound feed nuts are typically small ACME or trapezoidal nuts with a mounting flange, a dovetail or a keyed body, and they are one of the most common causes of backlash that no amount of gib adjustment will fix. Send the worn nuts and the matching screws and we will quote the set.
Lathe that cannot cut a thread? Send the worn half nuts plus a length of leadscrew — or photos, the screw’s major diameter at both ends and the TPI or pitch. Free drawing, honest advice on whether the screw needs replacing too, quote in 24–48 hours. Get a quote →
Send the worn half nuts and a length of leadscrew — threads cut to your actual screw, cast iron, bronze or brass. Quote in 24–48 hours.