Like Doc said, completely depends on the truck.
Generally I'll use a 9/32" or sometimes a K bit to chase it. I'll mic the axle to decide. I chuck a 9/32" transfer punch in the drill chuck, and use that to align the truck in the vice. I measure the knurl and will occasionally relieve the opening a little with an L bit so the truck doesn't split. Some trucks are more forgiving than others. Sure Grip's are, Ultimate's clearly are not.
While all that precision is certainly nice, in my estimation anyway, it's not sustainable in a skate application. There are too many cumulative production tolerances to make any sort of precise interchangeability feasible. Plus, once you've gone around a few corners, I can assure you that the axle has probably nudged a little in the truck.
I use a simple 1 ton arbor press to push 'em in. You get feedback from the lever than a hydraulic won't give you, so if something isn't quite kosher, you'll know it before you wreck something. Yes, there's an aluminum cap that protects the flip lever, and I take it nice and easy. Use a machinists rule to check centering.
As for shimming, I have good luck with this:
Not super scientific, but sure makes up for the slight variances that will naturally occur.