Tandem stoker stems
I'd like to fabricate a longer boom for a tandem stoker stem I currently own. It's a Control Tech stem made up of two pieces. One clamps to the captain's seat post and provides a ~5 inch female extension, and the other is a 28.6 mm (OD) boom that slides into the first piece and provides a quill-style handle bar clamp. I was thinking I would just replace the boom with a 28.6 OD length of 4130 and clamp a threadless stem to it. So, I have two questions:
1) Can anyone recommend the appropriate wall thickness? I was thinking 2.1 mm (0.083 in from Dillsburg Aero works).
2) I'll need to have the new boom powedercoated or painted to avoid corrosion. How much is this going to affect the fit? If I use something that already has a 28.6 mm OD, will it no longer fit once painted/powdercoated?