I was wondering what size pinvise do you use for the microscopic drill bit that comes with the BSRT wheel jig for pinning the rear axle? More importantly where do you buy one to fit this tiny bit? My pinvise collets are not small enough to hold this bit. Also are there any tips on drilling these holes?

use a .025" drill bit..it is a #70 ( I believe)

I found mine on EBay

Don't try to drill the entire hole through the gauge.

Put the chassis in the gauge, drill just enough to mark the locations, the pull the chassis out and continue drilling keeping a close on drill bit flex.

You need a micro pinvise for those small bits, try micromark.com

If you have a local hobby or train shop they should carry small pinvises