Custom Metric Thread Adapters

When the Metric Combination Isn't Stocked

A coarse M30×3.5 on one side and a fine M24×2 on the other is the point where the catalogue runs out. Standard metric reducers cover the obvious steps — and almost always within one pitch family; the moment your two ends differ in both diameter and pitch, the stock range ends. The threads are both perfectly standard; the part that joins them simply isn't a stock item, and bushing kits or hydraulic reducers won't help because those are built around sealing standards, not a plain mechanical link.

EKINSUN single-points each end to its own diameter and pitch on one body. We make custom metric thread adapters — mixed-pitch reducers, double-male studs and male-female adapters — in carbon steel, alloy steel or 304/316 stainless, with a hex or wrench-flat body so you can torque them. A single piece is normal work; there's no tooling cost on a machined adapter.

If your conversion is a standard one (BSP/NPT/metric in the usual sizes) start at thread adapters; if it's a gauge or transducer port, see sensor thread adapters. This page is for the non-standard, mechanical, mixed-pitch metric parts no one stocks.

A Real Job: M30×3.5 ↔ M24×2, Two Forms

Two short adapters, both 60 mm long, M30×3.5 to M24×2, mechanical only (no sealing), with flats for a spanner — a job we were recently asked to quote, and a good example of what this page is for:

Same two threads, two different jobs — one converts a female port to a male stud, the other joins two female components as a stud. Both are single pieces. That's the kind of part we quote in 12 hours; send us your two ends the same way.

Two Forms We Machine

Common Metric Reducing Combinations We Machine

Need a bigger thread? For the M33–M52 range in coarse and fine pitch, see large metric thread adapters.

These are the size steps customers ask for most. The pitches below are the standard coarse forms — but the reason to have one machined rather than bought is the non-standard case: a mixed pitch, an unusual material, an oversized body or a length no stock reducer offers. Standard sizes are simply the starting point.

Reducing adapter	Standard pitches	Made to order
M12 → M8	M12×1.75 → M8×1.25	The two-step thread reducer skipped by most catalogues — thin-wall, so we machine it with a hex or as a stud type
M12 → M10	M12×1.75 → M10×1.5	Fine pitches, longer body, stainless
M16 → M12	M16×2 → M12×1.75	Mixed pitch, hex flats, alloy steel
M20 → M16	M20×2.5 → M16×2	Fine-pitch ends, custom length
M24 → M20	M24×3 → M20×2.5	Mixed pitch, 316 stainless, standoff
M30 → M24	M30×3.5 → M24×3	Incl. mixed-pitch M30×3.5 → M24×2

Need a step that isn't listed, or a combination of two pitches that no catalogue stocks? That is exactly what we single-point to order — build your spec below or send the two thread designations and we quote it.

Why a Catalogue Reducer Won't Do It

The detail that defeats off-the-shelf parts is the pitch. Here's how we hold what matters on a mechanical metric adapter:

What's tricky	How we handle it
Different pitch each end	Each thread is single-pointed to its own pitch — 3.5 mm coarse one side, 2 mm fine the other — on the same part
Different diameter each end	The body is turned so both major diameters are fully formed without running out of material
Hex / wrench flats	Milled across the body, sized to a standard spanner where the diameters allow, so the part can be torqued
Engagement & overall length	Effective thread length each end and total length held to your spec (e.g. 20 mm + 20 mm within 60 mm)
Fit class	6g/6H by default; tighter or looser on request for a press, running or hand fit
Mechanical vs sealing	No seal feature for a plain mechanical joint; seal face or sealant allowance added only if you need it

Build Your Adapter Spec — Instant RFQ

Configure your metric adapter below — pick the thread and pitch on each end, the form, body and lengths. It generates clean RFQ text you can copy, or send straight to our engineers — no account, no CAD file.

Materials for Mechanical Adapters

Tell us the property class and we cut the part from the steel that carries it. One caveat first: ISO 898-1 gives a class to a fastener made and tested to that standard, marking included — a machined adapter has no head to stamp, so it carries its bar instead. The minima below are the ISO 898-1 numbers; the steel column is what the part is actually turned from. The full bolt grade chart carries the hardness and elongation rows as well.

Class you specify	Steel we turn it from	Rm min N/mm²	Rp0.2 min N/mm²
8.8	C45 (1045), 34Cr4 or 37Cr4 — quenched and tempered	800	640
8.8, thread above M16	Same steels, larger section	830	660
10.9	34CrMo4 (4135) or 42CrMo4 (4140) — quenched and tempered	1040	940
12.9	42CrMo4 (4140) or 34CrNiMo6 (4340) — quenched and tempered	1220	1100
A2-70 / A4-70	304 / 316 cold-drawn bar — corrosion first, strength second	700	450

Two things we say before you order rather than after. At a stud end of M8 or M12 the section is small and 42CrMo4 reaches 10.9 without argument; cut the same steel at a large diameter and it lands a class lower — we tell you the class the part actually makes instead of printing the one that was asked for. And the paperwork: the EN 10204 3.1 mill certificate for the bar comes with series orders, not with a single piece or a sample. If the certificate is the point of the order, say so and we quote the batch that carries it. Marking the part to ISO 898-1 with the full test regime is separate work — ask and we price it.

No Drawing? We Reverse Engineer It

One family of metric reducers has its own page because the sizes and the sealing are different: cable gland and conduit entries. M12 to M63 all run a 1.5 mm pitch there, the body usually has to be shortened to clear a cast housing, and PG threads sit deceptively close to metric without mating. Sizes, the PG conversion chart and the reducer-versus-enlarger question are on the cable gland & conduit adapter page.

What to Send Us

• The thread & pitch on each end — e.g. M30×3.5 female to M24×2 male (or a sample of each side)
• Whether it's male-female, double-male stud, or female-female
• Mechanical only, or must it also seal (and if so, medium and pressure)
• Body: hex, wrench flats or round — and any spanner size you want to fit
• Overall length and effective thread engagement each end (e.g. 60 mm overall, 20 mm + 20 mm)
• Material preference, quantity (one is fine) and delivery country

A pitch outside ISO 261 is machined the same way: the M27×2 to M27×1.75 adapter we built, with pre-planned pairings to M24, M20, G3/4 and M36, is the worked example.

Where the Metric Reducer Catalogue Stops

M12×1.75 → M10×1.5 in plain steel is a stock item; a different pitch on each end, or a two-step reduction such as M12 → M8, is not. Coarse-to-coarse reducing bushes in the common sizes are stock items — the list below is what the stock range cannot do.

What you need	In the catalogue?	How we machine it
M12×1.75 → M10×1.5, plain steel	Stocked	Standard coarse-to-coarse bush. Buy it off the shelf.
Different pitch on each end	No	Each thread is single-pointed to its own pitch on the same part — 3.5 mm coarse one side, 2 mm fine the other.
A two-step reduction such as M12 → M8	No	Skipping two sizes leaves a thin wall, so it is machined with a hex or as a stud type rather than a plain bush.
Fit class tighter or looser than 6g/6H	No	6g/6H is our default. State press, running or hand fit and we cut to it.
Effective thread length held on both ends	No	For example 20 mm plus 20 mm inside a 60 mm overall. Catalogue bushes have one length.
Hex flats sized to a spanner you already own	No	Milled across the body to your wrench rather than to a catalogue table.
Through-bore for a shaft, cable or fluid	No	Bore and both threads cut in one setup so they stay concentric.
Left-hand thread on either end	No	Not stocked at any metric size.
316 stainless or alloy steel at small diameters	Rare	Small stock bushes are plated mild steel. Material is open here.

Pitches above are the ones this page already lists for each size pair.

See also the fitting thread identification chart with the ISO 6149 / DIN 3852 metric port series, and compression fittings for the DIN 2353 tube-to-port pairings.

Frequently Asked Questions