what does "crank the nut" mean?

Answer 1

crank
mechanical device for transmitting motion: a device consisting of an arm or handle that is connected to a shaft at right angles, enabling the transmission of motion to or from the shaft.
A crank may be used for changing rotary motion to reciprocating motion or vice versa.

nut
fastening screwed onto a bolt: a piece of metal, usually square or hexagonal, with a hole in the middle, screwed on the end of a bolt as a fastening for it

Example: adjusting the skates:
You don’t crank it back too much, because if you loosen the nut too much, once you get the adjustment you want, you’re now trying to lock it into place. If you crank the nut too much you’re changing the adjustment you just worked for.

The key is to just loosen the nut one crank so there’s one crank to tighten it, that’s key to getting your adjustment. If you crank the nut too much, you’ve created a problem because you’re thinking you’ve got the adjustment but you don’t have it.

Answer 2

To tighten down a bolt. Term developed in sports dealing with skateboarding, skiing, and rollerblading. Cheers!