Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hi Matt. The head bolts on my M90 which was purchased in January of this year are M3x.5 They are of two different lengths. Four of them are 18mm long and two are 20mm long. The two longer ones are at the two and four o'clock position, and are used to fasten the brass lifter assembly for the exhaust valve.