Hi,
Be careful not to mix up JIC3/8x24 (UNF thread) fittings with M10x1.00, they seem to screw in each other, but they are absolutely not compatible! Most of the time, metric fittings have a small cut (notch?) on each edge of the hexagonal part, it is a good way to see the difference.
But if you have a Sierra set-up, no worries, it is M10x1.00 all around : all master cylinder ports, front callipers and rear drums wheel cylinders (and I'm almost 100% sure that rear callipers are M10x1.00 too, if it is a 4 disc set-up)
So the easiest is to plan all your bulkheads, tee-pieces, etc. in M10x1.00, so there will be no confusion possible.
If you want to install a hydraulic brake light switch, a good one is the one from the VW Beetle, as it is M10x1.00, so you can install it on a 3 x M10x1.00 tee-piece (it will need a copper washer to be sealed though because it does not have any seat).
BTW, did you receive my reply to your PM?
Good luck
