Triumph Steering Stem Nut, for use on Triumph models: 
T90 / T100 - (without nacelle) (1963-67)
5T / T100 / TRW / Trophy (1948-59)
6T / T110 / TR6 / T120 (1948-62)
T120 / TR6 / T110 (1963-66)
O.E.M: 97-0405 / H0405.
Thread: 26TPI Split Stem