Milton couplers say "MILTON" on the collar, beware of cheap imported junk.  These couplers are American made in Chicago.  

This listing is for FOUR MILTON BRAND #715 air coupler fitting.  These are "M" style fittings with 1/4" Female NPT pipe thread. Milton M-style “Kwik-Change" couplers and plugs will interchange with all manufacturers who comply with the dimensional requirements of military specification MIL-C-4109.  These couplers fit milton brand #727 and #728 plugs/nipples

These are HIGH QUALITY BRASS couplers MADE in the USA.