To allow this, 'M' is placed on such fittings (in addition to any watertight control already on them) and indicates that the 'user' must exercise control in gastight conditions only.
Ukuvumela oku, u `M' ubekwe kwizifakelo ezinjalo (Ukengezu nokuluphi na ulawule lokungengeni manzi elusele kukuze) ubenise ukuba umsebenzisi makesebenzise ulawulo kwimeke ezingangeni gesi kuphela.