The Compressed Gas Association (CGA) developed the Diameter-Index Safety System (DISS) to establish a standard for non-interchangeable, removable connections for use with Medical Gases (200 psi max.), Vacuum (Suction), and WAGD (Evacuation) Service. Non-interchangeable indexing is achieved by a series of increasing and decreasing diameters in the components of the connections. These specific diameters act in a key-like fashion, so that fittings within the gas service “family” (Vacuum and WAGD included) will connect only with their own “family members.” In place of diameter indexing, Oxygen (DISS 1240) has been assigned the long established 9/16"-18 thread connection as its safety standard.
Each DISS connection consists of a Body Adaptor, Nipple, and Nut (Fig. 1). As the diameters of the Body Adaptor (A & B) increase/decrease, the diameters of its mating Nipple (C & D) increase/decrease proportionally. In this way, only properly mated and intended parts fit together to permit thread engagement (Fig. 2). The DISS system is utilized on gas pressure regulator outlets, wall outlets, anesthesia equipment and respiratory therapy equipment. For additional information on the Diameter-Index
Safety System, please contact Medical Gas Fittings Online.
Gas Name Connection Number
Carbon Dioxide 1080-A
He-O2 mixture (I) 1060-A
Instrument Air (III) 2080
Medical Air 1160-A
Nitrous Oxide 1040-A
O2-He mixture (II) 1180-A
Vacuum (Suction) 1220
WAGD (EVAC) 2220
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Note: (I) - Heliox mixtures: Helium over 80%.
(II) - Heliox mixtures: Helium not over 80%.
(III) - Intended for the powering of medical devices unrelated to human respiration.