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

Basically, whichever engine you have, look at the piston diameter, and source the green o rings  with a 1mm cross section.  Example: your engine has a 15mm bore, you want a 14x15 (or 15x1, depending on vendor listing) o ring.  I did exactly this for the vertical hit and miss m93 engine, when they were selling rings for ridiculous prices, and got like ten of them shipped for two dollars.  Yes China, but they’re utterly dirt cheap from hydraulics or food handling outfits that use them in equipment as connector seals.