How do you tighten the end bearing nut?

I have had some slop in my machine and determined it to be the ballscrew's end cap bearing nut (the 13mm nut with the Blue Nyloc insert). I tightened out the slop but I don't know if I overtightened it.

How do you tighten this but not overtighten?

by the way my machine has the coupling and I used that to hold the axis screw still while tightening the nut. This worked well. But there's got to be a method to just get it tight enough and not too tight.

I'm a bit worried.

thanks!
Nick