I use a three inch piece of leftover glass from some previous laminated bows I made wrapped with 220 grit paper. I got 100 5/16 nocks from last year's St Jude's auction that are a bit snug on the strings I make. A dozen or so strokes gets me where I need to be. I have 93 left Wudstix👍

How tight is Too tight?   The answer is: You should be able to snap the arrow nock on the string and let the arrow hang off the string and hold it's own weight, but just tapping the string gently it falls off.   If you tell your string builder what nocks you are using, they should fit perfectly. I don't like messing with fitting nocks myself, but prefer sanding than bending them and using heat.   .02 cents worth   Kirk

Lots depends on the bowstring fiber thickness and strand count, and why I'll first try different Halo center serving fiber thicknesses from .016 to .025, get it as close as possible for a light nock grip to the serving.  The rest is up to the nock where I have different brands to try out for a good fit.  Last resort is sanding the nock groove to fit.  I'd always rather have an initial tight fit than a loose fit of the nock to the serving.