Bought a used bike with loose rear lock nuts on both sides. Normally when I repack bearings I'll leave the drive side alone, to serve as a guide when putting everything back together.
I am wondering if the rear axle spacing (exposed axle from locknut) should be the same on both sides? I've been looking at some articles/videos but can't seem to find the answer.
Any information would be appreciated.
Thanks.

How much past the lock nuts does the axle extend is a "depends" answer.

First is whether the axle is a QR design or an axle nuts design. Obviously the nutted version needs enough axle extension to allow for the drop out thickness (and der hanger plate, claw) and that of the nut so the nut is fully threaded on when tightened. Generally I aim for the same amount of axle showing past the nuts on both sides. For a QR axle the axle ends shouldn't extend more then that of the drop out thickness, and a bit less is the typical. Remember that the QR conical springs take up a small amount of space between the axle end and the QR end caps, you don't want the QR to not fully bite into the drop out because the axle/springs stick out too far.

As mentioned if the der is attached with a "separate of the frame" hanger (these days often referred as a "claw") the effective drop out thickness will be more then that of just the frame. So a bit more axle extension on the drive side in these cases is allowable.

I aim for about the same amount of axle extension on both sides unless something suggests otherwise. Andy

I aim for the same but if I am in a hurry I'll live with anything between just past the inside of the dropout to almost flush with the outside of the dropout. Basically the rule(s) are: don't ever hit the QR lever assembly or the QR locknut. As long as that never happens, everything else works. Too short is a PIA to get the wheel located right but does work just fine. The QR and locknut do all the work. The axle is doing nothing. (Now this may not be true of inferior QRs or QRs with non-steel skewers. Wouldn't know. I've always just used decent asymmetrical steel skewered QRs.)

Ben

The "standard" qr axle protrusion past the locknuts is 5.5 mm on both sides assuming the hub and axle are built for the same OLD. For example, a 130 mm OLD hub would use a 141 mm axle.

Physically it needs to be almost as wide as the dropout is thick ..

not quite all , that little QR spring gets a little space..