The size and pitch on an OEM transfer case shifter is 12 mm 1.25 pitch. The Marlin knobs screw right on with no problem. 
I think it's the same for the trans. I put a Hurst T handle on mine, but I had to make a bushing out of a 12x1.25 nut by ginding it down and pressing it into the T handle. It wasn't perfect but the handle is on there good, and I couldn't be happier.
