1/2″ NPT × BSP, Rc 1/2 × NPT and Rc 1/8 × Metric Adapters in Stock — 17 Pairs in 304 Stainless

Thread Adapters in Stock — 17 Pairs in 304 Stainless

Three families are in stock: 1/2″ NPT female to nine male threads (G 1/8 to G 1, R 1/2 and 1/2″ NPT), 1/2″ BSPT female (Rc 1/2) to four NPT male sizes, and 1/8″ BSPT female (Rc 1/8) to four metric male threads (M6×1, M10×1, M10×1.5, M20×1.5). All are hex adapters in 304 stainless steel (1.4301), supplied from 1 piece. EKINSUN LTD is a custom parts manufacturer that supplies these pairs from stock and machines any other thread pair to order from 1 piece: no CAD file is needed (a photo with caliper readings, or the old fitting, is enough), and a dimensioned drawing comes for approval before machining.

Thread data: NPT per ASME B1.20.1, BSP per ISO 228-1 (G, parallel) and ISO 7-1 (R male and Rc female, taper), metric per ISO 261. The female end is the thread inside the hex; the male end is the external thread. Dimensions of the Rc 1/2 × 3/4″ NPT pair are on the drawing below; ask for the drawing of any other pair.

Prices per Piece — All 17 Pairs, 304 Stainless

Prices exclude shipping. Shipping is about $30 (≈ €26) per parcel up to 0.5 kg, sent DDP door to door: import duties and taxes are paid, nothing is due on delivery. Dollar prices are converted at the ECB rate of 25 September 2026 (€1 = $1.1403) and rounded up. Several pairs in one order: ask for the combined price. Made-to-order pairs are quoted separately, within 12 hours.

Not the Pair You Need? Made to Order From 1 Piece

Any pair that is not in the stock table is machined to order, in 304 or 316L stainless, brass or aluminium, with the length and bore you need. The page for each thread family has the sizes, the sealing forms and what to send:

Measure Both Threads First — Then Stock or Made to Order

A thread adapter fits only if both threads are named right, and a wrong pitch is the usual mistake. Measure the outside diameter of the male thread with a caliper; then measure ten threads, from the 1st crest to the 11th, and divide by ten: 18.14 mm for ten threads is 14 threads per inch, 13.37 mm is 19 TPI, 10.00 mm is a 1 mm metric pitch. A taper thread (NPT, R) gets 0.63 mm smaller in diameter every 10 mm towards the tip (taper 1:16); a parallel thread (G, metric) measures the same along its length, and its fitting seals on a flat face. For a female port, measure a fitting that screws into it.

Two cases need more than a caliper: at 1/2″ and 3/4″, NPT and BSP both have 14 TPI, so the diameter (21.34 against 20.96 mm at 1/2″) and a 55°/60° thread gauge decide; at 1/8″, ten threads are 9.41 mm for NPT (27 TPI) and 9.07 mm for BSP (28 TPI). When the readings name a pair in the stock table, buy it from stock; when they do not, we machine the pair from 1 piece.

1/2″ NPT vs 1/2″ BSP — Why They Need an Adapter

A 1/2″ NPT and a 1/2″ BSP thread both have 14 threads per inch, so one can start in the other by hand. The angle (60° against 55°) and the diameter (21.34 mm against 20.96 mm) differ, and the joint leaks. See the fitting thread identification chart and BSPP vs BSPT vs NPT.

1/8″ BSP vs M10×1 — Close, Not the Same

A 1/8″ BSP thread is 9.73 mm across with 28 threads per inch (0.907 mm pitch); M10×1 is 10.00 mm with a 1 mm pitch. A caliper alone does not separate them: count the pitch, and check the angle (55° against 60°). Gauges and sensors come with either thread, which is why the Rc 1/8 × metric adapters are in stock.

How Each End Seals

The NPT ends and the R and Rc ends are taper threads: they seal on the thread, with PTFE tape or thread sealant on the male thread. The G ends and the metric ends (M6×1, M10×1, M10×1.5, M20×1.5) are parallel threads: they seal at the face, with a bonded washer or an O-ring clamped between the adapter’s shoulder and the flat face of the port, so the port needs a flat seat around the thread.

From Stock or Made to Order

The 17 pairs in the table are stock parts. Other pairs, other materials and other lengths are machined to order from 1 piece; the page for each thread family is in the made-to-order table above. One adapter with the right two threads replaces two stacked fittings (a reducing bush plus a thread converter): one threaded joint fewer to seal, and a shorter stack.

Will It Fit? Near Misses, and What to Do When the Pair Is Not Here

A 1/2″ NPT male will start in a G 1/2 port — both are 14 TPI — and bind two turns in: the NPT is 21.34 mm at the large end against 20.96 mm for G 1/2, and its 60° flanks sit on 55° flanks, so it never seals and usually damages the port. The same is true the other way round, and of a taper R 1/2 into a parallel G 1/2. If you cannot find an adapter for the exact pair anywhere — the odd ones are Rc 1/8 × M10×1 and 1/2″ NPT × G 5/8 — look in the table above first: both are in stock, in 304, from 1 piece.

What do I need to connect a 1/2″ NPT gauge to a G 1/2 port?

The 1/2″ NPT female × G 1/2 male adapter from the stock table: the gauge screws into the NPT end with PTFE tape on its taper, and the G 1/2 end seals on the port face with a bonded washer or an O-ring, not on its thread. For the reverse — a G 1/2 gauge into a 1/2″ NPT port — the pair is G 1/2 female × 1/2″ NPT male, which is not a stock part and is machined to order.

Same adapter, but in 316, longer, or with a bigger hex

The same pair in 316L for seawater or chemicals, a longer body to clear a boss, a larger hex or two spanner flats, the female and male ends swapped, or a pair that is not in the table at all is machined to order from 1 piece: quoted in 12 hours, 5 working days to make, the drawing approved by you first; say what differs from the stock part.

When your current supplier cannot: small quantities, a second source, repeat orders

If your current supplier asks for 100 pieces where you need 5, quotes six weeks for a stock part, or has stopped carrying the pair, the table above is the second source: 1–9 pieces at €25 each, 200 and up at €15, shipped DDP for about US$30 a parcel to Germany, France, the UK or the US with duty paid; a repeat order is the same pair at the same tier. For a yearly volume — “we need 300 a year, must be 304” — ask for a blanket price and call off as you go. Must it be 316? That is the made-to-order route above, same 1-piece minimum.

By Pair — Quick Answers

What adapter joins 1/2" NPT female to 1/4" BSP male?

A 1/2″ NPT female × G 1/4 male adapter, in stock in 304 stainless. G 1/4 is 13.16 mm with 19 threads per inch and seals at the face with a bonded washer.

What adapter joins 1/2" NPT female to 3/4" BSP male?

A 1/2″ NPT female × G 3/4 male adapter, in stock in 304 stainless; G 3/4 is 26.44 mm with 14 threads per inch.

Is there a 1/2" BSPT female to 3/4" NPT male adapter?

Yes, in stock in 304 stainless: Rc 1/2 female × 3/4″ NPT male, 35 mm long with a 28 mm hex.

Is there a 1/2" BSP to 1/8" NPT adapter?

Yes: Rc 1/2 female × 1/8″ NPT male, in stock in 304 stainless. For the other way round (1/8″ NPT female × 1/2″ BSP male) it is made to order.

Is there a 1/8" BSP female to M10×1 male adapter?

Yes, in stock in 304 stainless: Rc 1/8 female × M10×1 male; M10×1.5, M6×1 and M20×1.5 male versions too. A gauge or sensor with a 1/8″ BSP thread goes into the adapter, and the adapter into the metric port.

Is there a 1/8" BSP female to M20×1.5 male adapter?

Yes, in stock in 304 stainless: Rc 1/8 female × M20×1.5 male. The M20×1.5 end is a parallel thread and seals at the face with a bonded washer or an O-ring.

What adapter joins 1/2" NPT female to 1/2" BSP male?

Two 1/2″ NPT female adapters are in stock in 304 stainless, one for each kind of 1/2″ BSP male thread: R 1/2 male (BSPT, taper, seals on the thread) and G 1/2 male (BSPP, parallel, seals at the face with a bonded washer). Check which one the port takes: a G port has a flat face around the thread.

What adapter joins 1/2" NPT female to 3/8" BSP male?

A 1/2″ NPT female × G 3/8 male adapter, in stock in 304 stainless; G 3/8 is 16.66 mm with 19 threads per inch and seals at the face.

Is there a stainless steel BSP to NPT adapter?

Yes: all 17 pairs on this page are 304 stainless (1.4301), in stock from 1 piece. A 316L (1.4404) version of any pair is machined to order from 1 piece.

Is there a 3/4" BSP female to 1/2" NPT male adapter?

Not in stock: this pair is machined to order from 1 piece, in 304 or 316L stainless or brass, quoted in 12 hours. The made-to-order page is BSP to NPT adapters.

What to Send for a Price

The pair, female end first (for example “1/2″ NPT female × G 1/4 male”), the quantity and the country it ships to. For a pair that is not in the table, add the length you need, the material and a photo of the mating ports; no CAD file is needed, and you approve a dimensioned drawing before machining starts. Quote in 12 hours; production for made-to-order pairs is 5 working days for one to a few dozen pieces, and the courier takes 5–7 working days to Europe and North America.

Thread Adapters in Stock — FAQ