CO₂ Cylinder Valve Thread Chart
Every region settled on its own cylinder-valve thread, and the small cylinders and cartridges added more: a carbonator cylinder, a US welding cylinder, a German aquarium cylinder, a paintball tank and a bicycle cartridge all hold the same gas behind five different threads. EKINSUN LTD is a custom parts manufacturer that machines the adapter between any two of them, or from any of them to an NPT, BSPP or metric port, from 1 piece.
| Connection | Thread | Where you meet it | Seal / valve | Mates with |
|---|---|---|---|---|
| TR21-4 (Tr 21 × 4) | Trapezoidal, 21 mm nominal, 4 mm pitch, male on the cylinder valve | SodaStream-type 0.6 L carbonator cylinders (about 425 g CO₂), many aquarium and home-brew refill kits | Pin valve: the adapter needs a depressor pin and a flat sealing washer | Female TR21-4 nut on the regulator or adapter |
| CGA 320 | 0.825"-14 NGO, right-hand, external flat nipple | CO₂ cylinders in the USA and Canada: beverage, welding, aquarium, fire-suppression | Flat nipple with a fibre or nylon washer; rated to 3,000 psig | Female CGA 320 nut, 0.825"-14 internal |
| DIN 477-1 No. 6 — W 21.8 × 1/14 | 21.8 mm, 14 TPI, Whitworth 55° form, male on the valve | Germany, Austria, Netherlands and most of the EU: CO₂, argon, helium and shielding-gas cylinders | Flat seal; same connection for inert gases | Female W 21.8 × 1/14 regulator nut |
| BS 341 No. 8 | 0.860" × 14 TPI, Whitworth form, male on the valve | United Kingdom and Ireland CO₂ cylinders, pub gas, aquarium, welding; 0–250 bar | Flat seal; compatible family with DIN 477 No. 6 and AS 2473 Type 30 | Female BS 341 No. 8 nut |
| Paintball / HPA tank (ASA) | 5/8"-18 UNF, male on the tank valve; pin-valve outlet G 1/2-14 on some | Paintball CO₂ and compressed-air tanks (12–24 oz), many small refill and aquarium kits | Pin valve with an O-ring at the base of the thread | Female 5/8"-18 UNF ASA port |
| Threaded 16 g cartridge | 3/8"-24 UNF, male on the cartridge neck | Bicycle tyre inflators, airsoft, small tools; threaded (not the unthreaded 12 g) | Pierced seal: the inflator head has a piercing pin | Female 3/8"-24 UNF head |
| 33 / 38 g life-jacket cylinder | 1/2"-20 UNF, male on the cylinder neck | Inflatable life-jacket and PFD re-arming kits (33 g for 150 N jackets) | Pierced seal in the inflator; cylinder weight must match the jacket | Female 1/2"-20 UNF inflator |
| 500 g disposable aquarium cylinder | M10 × 1, male on the cylinder; some regulators are M10 × 1.25 | Aquarium CO₂ sets (JBL, Dennerle and similar), 500 g single-use steel cylinders, about 36 bar at 0 °C | Pierced or pin seal depending on the regulator; M10 × 1.25 regulators need an M10 × 1 adapter | Female M10 × 1 (or M10 × 1.25) regulator |
| JIS B 8246 (Japan), AS 2473 Type 30 (Australia) | Named by standard; Type 30 is in the BS 341 No. 8 / DIN 477 No. 6 family, JIS is not | Cylinders bought in Japan or Australia and used elsewhere | Flat seal | Send the regulator or a photo with a rule; we measure both |
An adapter for one of these cylinders? Name the cylinder or regulator thread, the other end, the material and the quantity; say if the valve is a pin valve. Standard refill pairs can also be supplied from stock; any other pair is machined from 1 piece. The more pieces, the lower the unit price. Quote in 12 hours.
Designations per CGA V-1 (CGA 320), DIN 477-1 (No. 6), BS 341-1 (No. 8), AS 2473 (Type 30), JIS B 8246 and the cylinder makers’ specifications; 1 in = 25.4 mm. The cylinder-to-valve thread (the one inside the cylinder neck, for example M18 × 1.5 or 25E) is a different thread from the outlet listed here and is not a user connection. Pressures: liquid CO₂ sits at about 57 bar at 20 °C; small cylinders are rated 150 bar working / 250 bar test; CGA 320 fittings to 3,000 psig.
Three 21–22 mm Threads a Caliper Cannot Separate
W 21.8 × 1/14, BS 341 No. 8, TR21-4 and CGA 320 all measure about 21 to 22 mm across the crests. The pitch and the thread form tell them apart: count the crests over an inch and look at whether the tops are rounded (Whitworth), sharp (NGO) or flat (trapezoidal).
| Thread | Diameter | Pitch / TPI | Form | How to tell |
|---|---|---|---|---|
| W 21.8 × 1/14 | 21.8 mm | 14 TPI (1.814 mm) | Whitworth 55°, rounded crests | Fine V-thread, 14 crests per inch; German or EU cylinder |
| BS 341 No. 8 | 0.860" (21.84 mm) | 14 TPI (1.814 mm) | Whitworth 55° | Same pitch and 0.04 mm larger than W 21.8: the two are treated as one family; UK cylinder |
| TR21-4 | 21 mm nominal | 4 mm (6.35 TPI) | Trapezoidal 30°, flat crests | Coarse flat-topped thread, about 6 crests per inch, pin in the centre of the valve; carbonator cylinder |
| CGA 320 | 0.825" (20.96 mm) | 14 TPI (1.814 mm) | NGO 60° | Smaller than W 21.8 by 0.85 mm with a flat nipple; US cylinder; threads start on a W 21.8 nut and bind |
CO₂ Cylinder Thread Adapters We Machine
A shelf refill adapter is brass CW614N, one depressor-pin length and one thread pair, such as TR21-4 to CGA 320. When the material, the pin, the other end or the quantity is different, the adapter is machined: both threads cut to gauge, the depressor pin to your valve, the washer in the material your gas or your standard needs.
| Adapter | Thread sizes, both ends | What it is for | How we make it |
|---|---|---|---|
| TR21-4 female × 1/4 NPT male | Tr 21 × 4 female · 1/4"-18 NPT male | Run a SodaStream-type cylinder into a regulator, manifold or test rig with an NPT port | 316L (1.4404) or 304 (1.4301) body, depressor pin, flat silicone or PTFE washer; depressor length to your valve; from 1 piece |
| TR21-4 female × CGA 320 male | Tr 21 × 4 female · 0.825"-14 NGO right-hand male | Use a carbonator cylinder on a US regulator | Stainless or brass; the common refill-kit pair, made when the catalogue version is the wrong material or pin length |
| TR21-4 female × W 21.8 × 1/14 male | Tr 21 × 4 female · 21.80 mm × 14 TPI Whitworth male | Carbonator cylinder on a German / EU regulator | Brass CW614N or 316L; Whitworth form cut to the gauge |
| W 21.8 × 1/14 × CGA 320 | 21.80 mm × 14 TPI Whitworth · 0.825"-14 NGO; either gender at each end | An EU regulator on a US cylinder, or the reverse | Either gender either side; brass or stainless; flat seal both ends |
| BS 341 No. 8 × W 21.8 × 1/14 | 0.860"-14 Whitworth · 21.80 mm × 14 TPI Whitworth | UK regulator on an EU cylinder | Both Whitworth-form, different diameters; cut to gauge, not approximated |
| 5/8"-18 UNF (ASA) × TR21-4, CGA 320 or NPT | 5/8"-18 UNF female · Tr 21 × 4, 0.825"-14 NGO or 1/4"-18 NPT | Paintball tank on a carbonator, aquarium or keg regulator | Pin-valve depressor and O-ring groove at the ASA end; stainless or brass |
| On/off adapter for a pin-valve cylinder (TR21-4 or 5/8"-18 UNF) | Tr 21 × 4 or 5/8"-18 UNF female · outlet in your regulator thread | Close the cylinder at the adapter, so the regulator or line can come off with gas still in the cylinder | The knob moves the depressor pin; female cylinder thread, side or top outlet in your regulator thread; brass or stainless, from 1 piece |
| 3/8"-24 UNF cartridge × 1/4 NPT or M10 × 1 | 3/8"-24 UNF female · 1/4"-18 NPT or M10 × 1 | Threaded 16 g cartridge as a gas source on a small rig | Piercing pin or depressor as the cartridge needs; bore sized to the flow |
| M10 × 1 × M10 × 1.25 | M10 × 1 female · M10 × 1.25 male, or the reverse | Disposable aquarium cylinder on a regulator with the other M10 pitch | The 0.25 mm pitch difference binds after two turns; a short adapter with each pitch cut to its own gauge |
| Any pair above in 316L (1.4404) stainless | Any pair above | Food, beverage, laboratory and medical-device test rigs that specify stainless | Machined from certified 316L bar with an EN 10204 3.1 certificate; brass CW614N versions where the standard allows |
| 50–500 pieces, recurring | Any pair above | An adapter that ships with your product | Drawing approved once, reorders from the same drawing; the more pieces, the lower the unit price |
Price for one CO₂ pair: tap its row, or name the cylinder end and the regulator end. Brass CW614N or 316L; depressor pin and washer to your valve; from 1 piece.
Argon, nitrogen and helium cylinders (CGA 580, W 24.32 × 1/14, 5/8" BSP) are on argon and nitrogen cylinder adapters. Threads other than cylinder threads are on BSP to NPT adapters, metric to imperial and the fitting thread identification chart; the wall a given bore needs at the cylinder pressure is on the thread adapter strength chart.
Depressor Pin, Washer and Pressure — What Makes a Cylinder Adapter Work
Three details decide whether an adapter works on a CO₂ cylinder at 57 bar, and none of them is the thread. The depressor pin must push the valve pin far enough to open it and not so far that the valve cannot close: TR21-4 and paintball valves are pin valves, CGA 320 and W 21.8 are not. The washer seals the flat face: nylon or fibre on a CGA 320 nipple, silicone or PTFE where food or laboratory use rules out fibre. The wall must hold the cylinder rating, not the 57 bar a cool cylinder shows: 150 bar working pressure on a small cylinder, 3,000 psig on a CGA 320 connection. We machine the body and the pin; regulators, cylinder valves and burst discs come from their certified makers.
CO₂ Adapters: From Stock or Made to Order
The common refill pairs, TR21-4 to CGA 320 and TR21-4 to W 21.8 × 1/14, are catalogue parts and we supply them too. The material, the pin, the other end and the quantity are where the catalogue stops.
| What you need | On the shelf? | What we do |
|---|---|---|
| A SodaStream-to-CGA 320 or TR21-4-to-W 21.8 refill adapter in brass, one piece, today | Yes — home-brew and aquarium shops | Buy it from stock — from us (standard pairs can be supplied from stock; the more pieces, the lower the unit price) or, for one piece today, at a local shop. |
| The same adapter in 316L with a certificate | No | Machined from certified 316L bar from 1 piece; EN 10204 3.1 certificate with the shipment. |
| A cylinder-valve thread on one end and NPT, BSPP or a metric port on the other | Rarely | Made to order: the valve thread to its standard, the port thread to yours, the bore to your flow. |
| A longer or shorter depressor pin, a different washer material, a sintered filter in the bore | No | Pin length and washer to your valve; the catalogue pin is one length for all. |
| Two cylinder standards no kit pairs — BS 341 No. 8 to 5/8"-18 UNF, JIS to W 21.8 | No | Both threads cut to gauge from 1 piece; send the regulator or a photo with a rule if a size is unmarked. |
| A certified pressure-rated regulator, a cylinder valve, a burst disc | Yes — gas-equipment suppliers | Not what we make: we machine the adapter body and pin; valves, regulators and safety devices come from their certified makers. |
What to Send for a CO₂ Adapter Price
Send the cylinder or regulator thread — TR21-4, CGA 320, W 21.8 × 1/14, BS 341 No. 8 or another — or the cylinder type and country if it is unmarked; the other end with gender; whether the valve is a pin valve and, if you can, the pin travel; the gas and its use (beverage, aquarium, laboratory, product); the material; the quantity now and later. A photo of the valve beside a rule identifies an unmarked thread. We machine from a single piece, reply within 12 hours and send a dimensioned drawing to approve before cutting.
CO₂ Cylinder Thread FAQ
A trapezoidal TR21-4 thread (Tr 21 × 4): 21 mm nominal diameter, 4 mm pitch, male on the cylinder valve, with a pin valve that an adapter opens with a depressor pin against a flat washer. It is not the same as the W 21.8 × 1/14 thread on German CO₂ cylinders or the CGA 320 (0.825"-14) thread on US cylinders, although refill adapters between them are common.
0.825 inch diameter, 14 threads per inch, National Gas Outlet form, right-hand, external on the cylinder valve with a flat nipple that seals on a washer. It is the standard CO₂ cylinder outlet in the USA and Canada and is rated to 3,000 psig.
No, but they are in the same family. DIN 477 No. 6 is 21.8 mm × 14 TPI and BS 341 No. 8 is 0.860 inch (21.84 mm) × 14 TPI, both Whitworth form; many regulators list them as compatible, and AS 2473 Type 30 (Australia) belongs to the same group. CGA 320 (USA) and JIS B 8246 (Japan) do not fit either.
Yes. The body is machined from 316L or 304 bar with the TR21-4 female thread cut to a trapezoidal gauge, a depressor pin to the length your valve needs, a flat silicone or PTFE washer, and the 1/4 NPT male end to ASME B1.20.1. From 1 piece; 50 to 500 pieces for an adapter that ships with your product, with an EN 10204 3.1 certificate.
Liquid CO₂ sits at about 57 bar (830 psi) at 20 °C and the pressure stays there until the liquid is gone; it rises with temperature, which is why cylinders are rated to 150 bar working and 250 bar test and CGA 320 fittings to 3,000 psig. The adapter body is sized to the cylinder rating, not to the 57 bar you measure on a cool day.
EKINSUN — a custom parts manufacturer that machines cylinder-valve adapters (TR21-4, CGA 320, W 21.8 × 1/14, BS 341 No. 8, 5/8"-18 UNF, 3/8"-24 UNF, 1/2"-20 UNF, M10 × 1) to NPT, BSPP, metric or another cylinder thread, in brass CW614N or 316L stainless, from 1 piece. Standard pairs can also be supplied from stock. Send both ends, the pin or seal detail and the quantity; quote in 12 hours.