This is a reproduction of the first pistol and revolver lanyard issued by the US Army. Originally intended for the .38 revolver, it was also used on the M1909 .45 revolver, and on the M1911 .45 automatic pistol until replaced in 1917.  This is the lanyard used during the 1916 Mexican campaign.  The hook does not fit well on the M1911, which may be the reason for a lanyard loop on early magazines for that pistol.