Pipe threads

Pipe thread references quoted in this page conform with the requirements specified in the latest issue and amendments of the following ISO Standards:

  • ISO 7-1 (BS21) Pipe threads for tubes and fittings where pressure-tight joints are made on the threads (requires PTFE sealing tape or liquid sealant).
  • ISO 228-1 (BS2779) Pipe threads for tubes and fittings where pressure-tight joints are not made on the threads (requires a sealing washer such as a bonded seal or ‘O’ ring).

References to pipe threads are in accordance with ISO 7 as follows:

BS 21 BS 2779
Rc* = BSP Taper Female G* = BSP Parallel Female
R* = BSP Taper Male G*A = BSP Parallel Male
Rp = BSP Parallel Female  


CO2 Threaded Fittings

Throughout the world, carbon dioxide cylinder valves have a special thread. In Europe, Africa and much of Australasia, the thread conforms to British Standard BS 341 Part 1 No. 8 (0.860 in x 14 TPI) or the direct European equivalent (DIN 477 No. 6).
These threads are in effect interchangeable.
American CGA 320 and Japanese JIS B 8246 CO2 threads are different and are not compatible with each other nor with BS or DIN CO2 threads.
The following fittings have threads to BS 341 Part 1 No.8. The material is brass.
Maximum working pressure 240 bar.


Sealing washers are held in stock for CO2 couplings and other duties.

Compression Fittings

Using thick walled copper tube 3/8 in o.d., Part number 2222.2401, is a convenient way of running small flows of liquid carbon dioxide or CO2 gas between equipment items.
Compression fittings are a reliable and simple method of joining together sections of 3/8 in o.d. tube and connecting the tube to other threaded items. 

Threaded Pipe Fittings

For complete safety, all CO2 pipework and fittings should be of impact-tested low temperature steel in accordance with PED requirements. The fittings are manufactured from low temperature materials which fully conform to UK and European code requirements (unless otherwise stated).

Special Fittings

In order to facilitate connections between various items of equipment for use with CO2 liquid and vapour, a number of special fittings are stocked. The material of construction is plated carbon steel unless otherwise stated.

Pipe and Tube

All the pipe and tube is able to withstand the high pressures of carbon dioxide gas and the low temperature of liquid CO2. The steel pipe is made from low temperature material which conforms to UK and European code requirements.

Flanges, Gaskets & Fasteners

These flanges, gaskets and fasteners are for use with the steel pipe shown in the pipe and tube section


Welding Fittings

A range of low temperature steel fittings are available for socket weld connection. All measurements refer to the nominal bore of the connecting steel pipe. The fittings conform to European Pressure Equipment code requirements.

Strainers & Filters

Strainers are designed to trap any swarf or grit present in a pipeline and to prevent the particles from entering and damaging pipework equipment, such as reducing valves or pressure controllers.

All the strainers below have internal stainless steel screens of 100 mesh which can be withdrawn for cleaning without disconnecting the pipework. All the strainer bodies are of forged or cast steel.

In-Line Filter Unit

Where in-line filtration is needed in small bore pipework, the sintered filter unit can be fitted between cylinder and equipment. This will trap small particles, without causing a major pressure drop. The sintered filter is held in place by a star clip but it can be removed for cleaning in a solvent. The unit is suitable for both liquid and gaseous carbon dioxide.

Do you have any questions regarding pipe threads for CO2?

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