Titleist has been using .355″ taper tips and has pretty much always used them in their irons. The shaft would only measure .355″ at the very tip. It would measure approximately .370″ where the shaft exits the top of the hosel. It would help to know which model Titleist irons you have? Unless these have been rebored or were a custom order it would be odd for them to use a .370″ parallel tip.