It is not so important which thread standard you use, as keeping it consistent with the rest of the engine if at all possible. I believe you can now buy metric bolts with reduced-size heads for model fidelity.

(My own project has dragged on so long it's gained a right mixture of BS, BA and Metric, making future servicing problematical.)

What does the drawing specify for the bolt material – but are they not studs and nuts?

You can use phosphor-bronze, but do not use brass.

Anyone here built a "Minnie", who can advise more specifically?

I made bronze bolts for mine as that is what it shows on the drawings and I did not know any better. If doing it now I would still use bolts but leave a dimple on the top to look like a bit of exposed stud as it's easier to remove a bolt than the studs if you ever had need to remove the cylinder.

6BA on the drawing but M3 would be OK if you are doing it in metric but would need 5mm or 4.5mm A/F

Edited By JasonB on 26/05/2022 18:12:02

I doubt you'll find them ready-made. By all means try but I think you will need make them. Do so in the lathe to obtain threads properly concentric with the rod.

To make it proper tiddly there should be about one-and-a-half turns of stud thread showing above the nut when all is fitted, and the stud end is slightly rounded off.

To fit them, it is worth making a simple stud-box from an suitable piece of hexagon bar and a screw.