frame#Ｈ11018 can you tell what year model?

[hdhikaru]

hi there,frame#Ｈ11018　can you tell what year model?

[Kozy]

Triumph Serial Numbers (classicenglishbikes.com)

[AFJ]

H11018 as a Triumph frame number would indicate a late 1959 frame for a unit type 350 or 500cc engine.
Not sure as to when in 1959 they went to the unit construction engine but the 350cc engine was always unit construction from 1957-on.