Custom Thread Adapters

When the Two Threads Just Won't Meet

Equipment from different countries and eras rarely shares a thread standard. You end up with a British BSP port on one side and an American NPT or a metric fitting on the other — and the adapter that bridges them isn't on any shelf. EKINSUN machines that part to order — call it a threaded adapter, thread converter or threaded connector, it's the same job — with the correct thread and seal on each end.

Give us the two threads (or a sample of each side) and the medium it carries; we make the link that fits and seals. Fitting is the easy half — the sealed parts we machine is the part no catalogue covers once one end is non-standard.

Conversions We Machine

Common Conversions & Special Threads

The combinations engineers ask us for most — each machined to order in the size, hand and material you specify:

Conversion / type	Typical use
NPT ↔ metric	Joining US/imperial-threaded equipment to ISO metric ports — e.g. a custom 1/4" NPT to M12×1.5 thread adapter
BSP ↔ UNF	British pipe thread to UNF/UN fine, common on imported machinery and instrumentation
Left-hand thread adapters	LH threads for gas (fuel/acetylene), rotating shafts and anti-loosening joints — single-point cut to the exact hand and pitch
Custom / non-standard pitch	Odd or obsolete pitches converted or reproduced when no standard tap or die exists — cut to your measured pitch

Not sure of the exact standard, hand or pitch? Send a sample and we identify it for you — see how we reverse engineer an unknown thread.

Metric size conversions — M6, M8, M10, M12 and up

Stepping between two metric sizes is the request we machine most often. An M8 to M10 thread adapter, an M8 to M6 reducer or an M10 to M12 step-up bush — male-to-female, male-to-male or female-to-female, in standard or fine pitch:

Size pair	Notes
M6 ↔ M8	Small fixtures, camera and lamp mounts, sensor bosses — either direction, any pitch
M8 ↔ M10	The most requested pair — mirror stems, machine feet, stud extensions
M10 ↔ M12	Automotive sensors, hydraulic ports, mounting studs — standard or fine pitch (M12×1.25 / M10×1)
M12 ↔ M16 and larger	Structural studs, tooling, machine spindles — solid one-piece adapters up to M100

Every adapter is turned from solid and single-point threaded, so any pair and pitch is available — including combinations no catalogue stocks. One piece is fine.

Cable gland thread adapters

Enclosure entry doesn't match your gland? We machine cable gland thread adapters and reducers — metric (M16, M20, M25, M32) to PG, NPT or BSP, in brass, nickel-plated brass, stainless or aluminium, with O-ring seats or sealing washers to preserve the IP rating. Enlarger and reducer styles, short-pattern for shallow enclosures, one-off or batch. Full size charts, the PG-to-metric conversion table and the sizes we cut most are on the cable gland & conduit adapter page.

Buying in French or Spanish? The same adapters are covered in adaptateurs de filetage sur mesure and adaptadores de rosca a medida, with local thread standards and terminology.

The Full Conversion Map — Every Standard Pair We Machine

This is the whole family in one table. Where a pair has its own page, the link goes to sizes, seal guidance and real examples for that conversion; every other pair is machined to order from the same bar stock — the absence of a page never means the absence of the part.

Conversion pair	What it solves	Details
Metric ↔ metric (size steps)	Mounting a smaller-threaded part in a larger tapped hole — sensors, glands, repairs	Metric adapters · dedicated pages from M12→M10 up to M40→M32
Coarse ↔ fine pitch, same diameter	M10×1.5 hole, M10×1.25 part — the classic mismatch that looks identical until it jams	Pitch conversion
Metric ↔ NPT	US equipment into ISO metric ports and the reverse	Metric–imperial · large sizes M50–M100 to NPT
Metric ↔ G (BSPP)	European hydraulic and pneumatic ports — parallel thread, bonded-seal face	Metric–imperial · hydraulic adapters
Metric ↔ UNF / UNC	US fine and coarse unified threads on sensors, instruments, fasteners	13/16-28 UN→M20 worked example
BSPP ↔ NPT and BSPT ↔ NPT	British parallel or taper pipe to American taper — never interchangeable despite matching sizes	BSP–NPT adapters
JIC 37° ↔ metric / BSPP / ORFS	Hydraulic hose ends between two brands' systems, obsolete machine ports	Hydraulic adapters
Whitworth BSW / BSF ↔ metric	Pre-1970s British machinery, motorcycles and machine tools meeting modern metric parts	Whitworth conversions
Pg ↔ M cable glands	Legacy Panzergewinde enclosures taking modern metric glands	Cable gland adapters
Tri-clamp ↔ thread	Sanitary ferrule to threaded pipe, in the size your line actually has	Tri-clamp adapters
Hose barb ↔ thread	Hose tails in odd sizes and metric threads no catalogue stocks	Hose barb adapters
Gauge threads — M20×1.5, G, NPT, ZG	European instrument into American port and every reverse	Gauge adapters · sensor adapters
AN ↔ NPT / metric	Fuel and oil line conversions on engine swaps and imports	Fuel line adapters
Left-hand ↔ right-hand	Gas fittings, turnbuckles, rotating shafts — LH cut to any of the pairs above	Machined to order, any standard
Obsolete or unidentifiable	The thread no chart names — measured from your part, then mated	Identifying an unknown thread

Lookalike Threads That Do Not Mate — the Pairs an Adapter Exists For

Most adapter enquiries start with two threads that look the same and are not. G 1/2 measures 20.955 mm across the thread and 1/2 NPT measures 21.336 mm; M14 × 1.5 is 14.000 mm and 9/16-18 UNF is 14.288 mm. Pairs like these start by hand and then jam or strip. The rule: if the major diameters are within about 0.5 mm and the pitches within 0.3 mm, the threads will engage a few turns and fail — they need an adapter, not force.

Lookalike thread pairs: major diameter, pitch and flank angle side by side

Thread A	Thread B	Difference Ø · pitch	Do they mate?	What bridges them
G 1/2 (BSPP) 20.955 mm · 1.814 mm pitch · 55°, parallel	1/2 NPT 21.336 mm · 1.814 mm pitch · 60°, tapered	0.381 mm · 0.000 mm	No — same 14 TPI, but 55° against 60° and a taper against a parallel: the threads bind after a few turns and never seal	BSP → NPT adapter (see the conversion map above)
G 1/4 (BSPP) 13.157 mm · 1.337 mm pitch · 55°, parallel	1/4 NPT 13.716 mm · 1.411 mm pitch · 60°, tapered	0.559 mm · 0.074 mm	No — 19 against 18 TPI, the pitches drift apart within three turns	BSP → NPT adapter
G 1/8 (BSPP) 9.728 mm · 0.907 mm pitch · 55°, parallel	1/8 NPT 10.287 mm · 0.941 mm pitch · 60°, tapered	0.559 mm · 0.034 mm	No — 0.56 mm apart on diameter and one thread per inch apart on pitch	BSP → NPT adapter
M14 × 1.5 14.000 mm · 1.500 mm pitch · 60°	9/16-18 UNF 14.288 mm · 1.411 mm pitch · 60°	0.288 mm · 0.089 mm	No — starts by hand, jams after two turns; the classic sensor-port mix-up	metric → UNF adapter
M12 × 1.5 12.000 mm · 1.500 mm pitch · 60°	1/2-20 UNF 12.700 mm · 1.270 mm pitch · 60°	0.700 mm · 0.230 mm	No — 0.7 mm apart on diameter, 0.23 mm apart on pitch	fuel-line / brake-line adapter
M10 × 1 10.000 mm · 1.000 mm pitch · 60°	3/8-24 UNF 9.525 mm · 1.058 mm pitch · 60°	0.475 mm · 0.058 mm	No — the UNF is 0.475 mm smaller and rattles in the metric port	fuel-line / brake-line adapter
M22 × 1.5 22.000 mm · 1.500 mm pitch · 60°	7/8-14 UNF 22.225 mm · 1.814 mm pitch · 60°	0.225 mm · 0.314 mm	No — diameters 0.2 mm apart, pitches 0.3 mm apart; strips the softer part	custom metric thread adapter
M8 × 1.25 8.000 mm · 1.250 mm pitch · 60°	5/16-18 UNC 7.938 mm · 1.411 mm pitch · 60°	0.063 mm · 0.161 mm	No — a 5/16 bolt runs loose in an M8 nut; an M8 bolt does not enter a 5/16 nut	metric → imperial adapter
M6 × 1 6.000 mm · 1.000 mm pitch · 60°	1/4-28 UNF 6.350 mm · 0.907 mm pitch · 60°	0.350 mm · 0.093 mm	No — 0.35 mm apart on diameter, 0.09 mm on pitch	metric → imperial adapter
M5 × 0.8 5.000 mm · 0.800 mm pitch · 60°	10-32 UNF 4.826 mm · 0.794 mm pitch · 60°	0.174 mm · 0.006 mm	No — pitches almost equal, diameter 0.17 mm off: a 10-32 screw threads loosely into M5 and strips it	metric → imperial adapter

Where can I buy a thread adapter for one of these pairs?

For G-to-NPT in the common pipe sizes, hydraulic and pneumatic suppliers stock adapters — buy those, they are cheaper than a machined one. EKINSUN LTD is a custom parts manufacturer and machines the pairs the shelf does not hold: metric-to-UNF sensor and fuel-line sizes, fine pitches, a left-hand end, a specific hex or length, or an adapter that also seals with an O-ring or a cone — from your two thread callouts or from the two parts themselves, MOQ 1, quote in 12 hours. British sizes on old machines are identified first with the Whitworth thread chart; the clamp screws on the assembled joint are tightened from the metric bolt torque chart.

Material & Finish Options

We machine thread adapters in the material your line demands, with finishing to match:

• 316 stainless — corrosion, marine, chemical and food-grade lines (316 machining)
• 303 / 304 stainless — the default when you say “stainless” but the line is not marine or chemical; 303 cuts the cleanest threads and hex flats
• Brass — general fluid, air and water, available in small batches with no strict MOQ
• Aluminium 6061 / 7075 — where weight matters, with optional anodised finish for wear and corrosion resistance
• Carbon / alloy steel — for higher-pressure and hydraulic builds (see hydraulic adapters)

Getting the Seal Right

An adapter only earns its place if it doesn't leak. We machine the correct sealing feature for each standard:

Thread	How it seals
NPT / BSPT	Tapered thread — seals on the thread flanks (PTFE/sealant aided)
BSPP (G)	Parallel — seals on a bonded washer, O-ring or 30° cone
JIC / SAE	37° flare cone / O-ring boss
Metric	Flat, cone or O-ring depending on the port

Note that BSPT and NPT look similar but differ in taper and thread angle, so they aren't interchangeable — we machine a true converting adapter, not a forced fit.

Real parts from our shop

A few thread adapters that recently left our machines — click any photo to enlarge.

One job is written up in full, numbers and all: a one-off M30×1.5 to M12×1.75 female-female adapter in 316/316L, 46 mm hex across flats, 60 mm long, both holes blind, with 15 mm of full-form thread over a 16 mm hole floor at the large end. The enquiry specified fit class 6g on a female thread — an external-thread class that cannot apply to a hole — and we raised it as a query on the drawing instead of changing it silently; the buyer confirmed 6H. That form has its own size table: female-to-female adapters, M6 to M64.

Adapter, Adaptor, Bush or Nipple — What to Call It When You Search

The same part goes by different names depending on where you buy: US catalogues say adapter, UK and Australian suppliers write adaptor; a female-to-male step-down is a reducing bush (or reducer bushing), a double-male is a hex nipple, and a two-standard conversion is a transition fitting. Whichever word your trade uses, it is the same job to us: two thread specifications and a body between them, made to order — machined from bar, one piece or a production batch. If you don't know what your part is called, skip the name and send the two ends it must connect.

One body shape earns its own page: the hexagon. A male hex thread adapter (hex nipple), a male-female hex bushing or a female hex coupler is the same conversion with wrench flats machined on — standard SW widths, odd spanner widths and the large milled hexagons past SW 46 are covered on custom hex thread adapters.

One machine family also earns its own page: wood lathe spindle thread adapters — headstock noses the insert charts do not list, left-hand outboard threads, and repair sleeves for damaged noses.

Threads the Conversion Map Above Does Not Cover

The map above lists the standard pairs. These are the ones buyers send us because no standard names them — and because no catalogue carries them at all.

What you need	In the catalogue?	How we machine it
A pair already in the map, common size, plain steel	Often stocked	If a stockist lists it, buy it off the shelf. We are worth calling when the pair, the pitch or the material is not on their page.
ACME or trapezoidal on one end	No	Power-transmission thread forms are not fitting threads. Single-point cut to the lead and flank angle you give us.
Buttress thread — drum, tote and container ports	No	Container threads are coarse, asymmetric and rarely in any fitting catalogue. Cut to the profile of the port you send.
NPSM or a straight pipe thread against NPT taper	Thin	Straight-to-taper is the pairing people assume is interchangeable. It is not, and stock lists rarely carry the adapter.
A milk tank, liquor bottle or vessel thread to NPT	No	One-off vessel threads measured from the part, then mated to whatever standard your line uses.
Left-hand on one end, right-hand on the other	No	Turnbuckle and gas-fitting logic in a thread adapter. Cut like any other pitch — full family on left-hand thread adapters.
The same conversion as a brass thread adapter, or in 316 stainless	Common sizes in plated steel, if at all	Turned to the same gauges in brass CuZn39Pb3 / CW614N (US ≈ C360) or 316L — a stainless steel thread adapter costs the metal, not a redesign.
A thread that no chart names	No	Measured from your part — pitch, major diameter, flank angle and taper — then mated. This is the job we were set up for.

If your pair is in the map above, that page or a stockist is usually the faster route.

Two of the jobs in this table are written up start to finish, drawing included: a custom thread adapter from a hand drawing — M30×3.5 to M24×2, and a mixed UNF / UN / metric stud coupler from a drawing. If all you have is a sketch or a photo, that intake has its own page: thread adapters from a sketch, no CAD needed.

Frequently Asked Questions