# NIST, DISS and probe-type medical gas connectors

Under ISO 18082 and CGA V-5, NIST and DISS are threaded, gas-specific connectors; probe-type terminal units fall under ISO 9170-1, which does not specify probe dimensions, and in the HTM 02-01 (2026) gas-specificity test only the correct gas probe enters the collar and locks in the terminal unit.

CGA V-5 lists automatic quick coupler valves among the existing means that DISS supplements but does not replace, and HTM 02-01, in its chapter on mobile vehicles, asks for connections on a quick-release medical gas specific probe. The table compares NIST and DISS with probe-type terminal units, into which a gas-specific probe enters and locks. HTM 02-01 describes NISTs as designed to prevent cross-connection, CGA describes DISS as noninterchangeable connections, and ISO 9170-1 aims to prevent the interchange of terminal units between gases.

|  | NIST | DISS | Probe-type terminal unit |
|---|---|---|---|
| Defined by | ISO 18082:2014 + Amd 1:2017 (revision at DIS stage) | CGA V-5, 7th edition (May 2019, reaffirmed March 2026) | ISO 9170-1:2017 for terminal units; probe dimensions in national standards such as BS 5682, DIN 13260-2 and NF S90-116 |
| How it connects | Non-interchangeable screw thread; HTM 02-01 says NISTs incorporate a check valve for all pressure gases | Removable threaded connections, readily and commonly engaged or disengaged in routine use and service | Only the correct gas probe enters the collar and locks in the terminal unit, and a pull test checks that it is retained (HTM 02-01) |
| Where the sources place it | HTM 02-01: on line valve assemblies and AVSUs, above medical supply units for flexible hoses, for gas testing and emergency backfeeding, and for carbon dioxide outlets | CGA: often on regulators, resuscitation, anaesthesia and therapy equipment; CGA does not designate where DISS should be applied | HTM 02-01: wall-mounted terminal units, where the probe should not swivel, and pendant or boom terminal units, where it must be free to rotate |

## NIST

ISO 18082 specifies the dimensions, allocation and marking of non-interchangeable screw-threaded (NIST) connectors for operating pressures up to 1 400 kPa, and for vacuum systems at pressures not greater than 60 kPa absolute; its list of gases includes oxygen, nitrous oxide, medical air, helium, carbon dioxide, xenon, oxygen-enriched air and air for driving surgical tools. ISO expects the 2014 edition to be replaced by ISO/DIS 18082. In HTM 02-01, where carbon dioxide is specified, a NIST connection is required rather than a probe connection. Open Critical Care notes that ventilator connections vary but NIST connectors are common, and that most ventilators come with a high pressure hose with a NIST fitting on one or both sides.

## DISS

CGA V-5, the Compressed Gas Association standard for the Diameter Index Safety System, defines noninterchangeable removable connections for medical gases at pressures of 200 psi (1380 kPa) or less. CGA says DISS supplements but does not replace the existing means of medical gas identification, the Pin Index Safety System, threaded cylinder valve outlet standards or automatic quick coupler valves. WHO's Foundations of medical oxygen systems (2023) also lists DISS among the connector styles used for wall outlets.

## Probe-type terminal units

ISO 9170-1:2017 sets out gas-specific assembly, mechanical resistance, flow, leakage and pressure drop of terminal units and aims to prevent their interchange between gases, but it does not specify the dimensions of probes. National styles differ: WHO (2023) shows the French NF S90-116, German DIN 13260-2, British BS 5682, Japanese, Australian and American styles; according to WHO, each style is a key-like non-interchangeable indexing system, so that fittings within a gas service connect only with their own type. NHS England's HTM 02-01 asks for terminal units conforming to BS 5682 and BS EN ISO 9170-1, and Part B notes that such terminal units incorporate an automatic isolating valve (check plate) in the first-fix assembly.

## Ultra Controlo outlets

Ultra Controlo medical gas wall outlets (Type B) are available in "Schraeder", NIST, DISS and DIN configurations for oxygen, compressed air, vacuum, nitrous oxide and anaesthetic gas evacuation, and its oxygen and air flowmeters connect directly to NIST, DISS and "Schraeder" wall outlets.

### What connection does HTM 02-01 ask for on a carbon dioxide outlet?

HTM 02-01 (2026) says that where carbon dioxide is specified, a NIST connection is required, not a probe connection, so it should be placed at the outermost point of the outlet array.

### Are probe styles the same in every country?

No. ISO 9170-1 does not specify probe dimensions, and WHO (2023) lists national styles such as the French NF S90-116, the German DIN 13260-2 and the British BS 5682.

## Sources

- [ISO 18082:2014, Dimensions of non-interchangeable screw-threaded (NIST) low-pressure connectors for medical gases (iso.org)](https://www.iso.org/standard/61329.html)
- [CGA V-5, Standard for Diameter Index Safety System (7th edition, May 2019, reaffirmed March 2026), publication page](https://legacy.cganet.com/Publication/Details.aspx?id=V-5)
- [ISO 9170-1:2017, Terminal units for medical gas pipeline systems (iso.org)](https://www.iso.org/standard/67451.html)
- [NHS England, HTM 02-01 Part A (2026 edition), paragraphs 3.9, 3.20, 3.53, 15.124, 15.127, 19.271 and 21.17](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [NHS England, HTM 02-01 Part B (2026 edition), paragraph 7.21 and quarterly terminal unit tasks](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-b-operational-management-aug-26.pdf)
- [WHO, Foundations of medical oxygen systems (17 February 2023), section 2.9.2 and Fig. 2.29](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [Open Critical Care, Oxygen FAQ: How can I connect an oxygen cylinder to a device that needs high pressure?](https://opencriticalcare.org/faq/how-can-i-connect-an-oxygen-cylinder-to-a-device-that-needs-high-pressure-eg-ventilator/)
- [DIN 13260-2:2025-06 (DIN Media)](https://www.dinmedia.de/en/standard/din-13260-2/389570410)
- [AFNOR, NF S90-116 (October 2020)](https://www.boutique.afnor.org/en-gb/standard/nf-s90116/medical-gas-pipeline-distribution-systems-sockets-and-related-probes-for-me/fa191757/260496)
- [Ultra Controlo, Medical Gas Wall Outlets (Type B)](https://www.ultracontrolo.com/accessories/medical-gas-outlets-2)
- [Ultra Controlo, medical oxygen and air flowmeter](https://www.ultracontrolo.com/accessories/flowmeter)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/compare/nist-vs-diss-vs-probe-connectors/