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

You may be SOoL on that one Gil .... I've checked all my normal Sci-Tech and Industrial outlets and can only find 4mm & 5mm with nothing in between. 11/64ths would be in that ballpark, but I don't see that anywhere either. Perhaps you can find where Stuart gets their tubing to find longer pieces in that diameter.

Perhaps just fitting packing material around the smaller sized tubing to where they are sealed in the oversized fittings?

Or ...... bore out the fittings to where they will accommodate 5mm or 3/16ths O.D. tubing!?!?

I'm pretty sure that you really don't wish to modify the originality in any way ..... but Tom Sr. wouldn't hesitate to do so!