(1) At the time of the initial boiler inspection, the state boiler inspector will assign and apply to the boiler a state identification number as directed by the department.

(2) Each steel boiler will be stamped by the inspector, utilizing letters and figures not less than 5/16" in height and arranged as follows: MTB 00000.

(3) Each cast iron boiler will be marked with a permanent marker in two locations and arranged as follows: MTB 00000.

(4) State identification numbers applied to boilers shall be maintained so as to be legible. When a boiler's state identification number becomes indistinct, the department will require the original number to be reapplied.