Custom Male-to-Male Thread Adapters

What a Male-to-Male Adapter Does

A male-to-male (double-male) adapter is a short machined stud with an external thread on both ends. It solves three jobs a catalog rarely covers at once: joining two female ports, extending a stud, or converting one male thread to a different male thread — for example bringing an M12×1.5 male end out to a 1/4" NPT male end. Because each end is turned independently, the two threads can be any combination you need.

This is a different form from a female-to-male reducer (which screws over a male thread) and from the general forms compared on our thread adapter types guide — start there if you are not sure which gender you need.

Ends We Combine

Any two of these on one stud, parallel or tapered, coarse or fine, right- or left-hand:

Thread family	Examples	Standard referenced
Metric	M6–M48, coarse & fine (M12×1.5, M20×1.5…)	ISO 261 / ISO 68-1 / DIN 13
Unified inch	UNC, UNF, UNEF — ¼"–2"	ASME B1.1
BSP parallel (G)	G1/8–G2, sealing on washer/O-ring	ISO 228-1 / BS EN ISO 228
BSP taper / NPT	Rc/R, 1/8–2" NPT, self-sealing	ISO 7-1 · ASME B1.20.1
Whitworth	BSW/BSF for legacy machinery	BS 84

Which Material? Cost, Corrosion & Sealing

An adapter's material sets its cost, corrosion resistance and how it seals and machines. Most go out in brass or stainless; the job decides:

Material	Density	Why choose it for an adapter
Brass (CZ121 / C360)	8.5 g/cm³	The default — free-machining, good sealing, low cost, non-sparking
Stainless 304	7.9 g/cm³	The most common all-round stainless — general corrosion (303 free-machining on request)
Stainless 316L	8.0 g/cm³	Marine, chemical and washdown; the workhorse for harsh media
Steel (zinc-plated)	7.85 g/cm³	High-pressure hydraulic strength at low cost
Aluminum 6061	2.70 g/cm³	Light, for low-pressure and weight-sensitive use
Titanium Gr5	4.43 g/cm³	Light, very strong and corrosion-proof — premium and aerospace

The Jobs That Land on Our Bench

Every size pair we machine — M6 to M64

Each row is a pair, with the numbers that decide the part. The Also written column carries the naming both ways round, because roughly half of enquiries name the small thread first. Coarse-to-coarse is listed at every size step; fine pitches are listed on the large end throughout and on both ends within three steps. A pair that is not listed is machined the same way — the table stops for readability, not for capability.

The step per side is where a male-to-male part fails when it fails. It is a stress raiser under bending, so the shoulder gets a radius rather than a sharp corner, and the thread cannot be cut right up to it: allow about two pitches of runout at the large end, or specify an undercut if the mating face has to seat flat against the shoulder.

Where the catalogue stops on this part

On material: 1.4301 covers general work and 1.4404 is the one to specify for salt or chemicals; 1.4305 free-machining stainless saves money where the part is nearly all thread. 7075 and 6061 are available and make sense on weight-driven jobs, but an adapter is a part that gets spannered, and aluminium threads gall long before stainless does — if the joint gets a torque figure, we quote steel or stainless and say why.

What one of these costs

Why every part is priced differently

There is no catalogue number to look up, so the quote is built from the part. These are the eight things that move it, roughly in order of how much they move it:

• Machining time — Both ends are single-point turned, and the part has to be turned round, parted and re-gripped to reach the second end. That second setup, not the threads themselves, is usually the biggest line in the cycle.
• Material — 1.4305 cuts fastest on all-thread parts; 1.4404 is for salt and chemicals; 42CrMo4 appears when the adapter carries real tension and the threads have to be rolled or cut in a heat-treated bar.
• Part dimensions — Stock is bought to the larger thread. The step per side is machined away, so a large step means more metal turned into swarf - an M42 to M12 adapter throws away most of the bar.
• Tolerance — 6g both ends is standard. Where the shoulder has to seat square to the thread axis, squareness becomes a called-out tolerance and it is checked, which adds time.
• Geometry — The shoulder radius and the thread runout are what make this part more than a stud. An undercut so the mating face can seat flat is an extra tool and an extra pass.
• Surface finish — As-machined is included; the flats are usually left as turned. Plating on a threaded part needs the thread cut oversize to allow for the coating, which has to be agreed before cutting.
• Quantity — The second setup is what a batch amortises. Between one piece and ten, that is where the unit price falls.
• Inspection — Go/no-go on both threads, and on adjuster versions a check that the two hands are marked correctly - that mark is what stops it being fitted backwards on site.

Which is why the honest answer to “what does a thread adapter cost” is a question back: two thread designations, the length, the material and how many. With those four we quote within 12 hours, and we quote the part you actually need rather than the nearest thing in a catalogue.

Need the body hexagonal? A double-male with a centre hex is a hex nipple — SW widths, naming and the large milled hexagons are on custom hex thread adapters.

And when the joint rotates, one of the two male ends is cut left-hand — the turnbuckle rule. That whole family lives on left-hand thread adapters.

Frequently Asked Questions