ðɪs ɐdˈɪʃənəl sˈeɪfti dɪvˈaɪs wʌz ˈædᵻd tə pɹədˈʌkʃən ɪn nˈaɪntiːnhˈʌndɹɪd sˈɪkstiːn ɔːɹ nˈaɪntiːnhˈʌndɹɪd sˈɛvəntˌiːn ɪnðə lˈæɾɚ wˈʌnhˈʌndɹɪd θˈɜːɾi nˈaɪn,zˈiəɹoʊzˈiəɹoʊ zˈiəɹoʊ sˈɪɹiəl nˈʌmbɚ ɹˈeɪndʒ, ænd pˈæʔn̩ɾᵻd baɪ kˈoʊlt ɪn nˈaɪntiːnhˈʌndɹɪd sˈɛvəntˌiːn.
This additional safety device was added to production in 1916 or 1917 in the latter 139,000 serial number range, and patented by Colt in 1917.