Abstract: A mounting adaptor for coupling a gas pressure regulator outlet to a gas meter inlet includes a plate having through-bores alignable with internally threaded blind holes which surround the meter inlet in the meter wall. The plate has a planar surface surrounding the outlet opening of the regulator and is adapted for contact engagement with a planar surface on the meter exterior wall surrounding the inlet opening. A groove in the planar surface of the plate holds a sealing ring to effect a seal. In an alternate construction, a tube extends from the plate into the meter inlet opening and an annular groove on the tube exterior holds a sealing ring for engagement with a cylindrical wall extending into the meter from the inlet opening.