I have just about every size serving there is, and for the strings I make for my lighter bow, I just can't get the exact right diameter, I wrap the area with dental floss and it really lasts for a long long time. I learned how to do it from the string making video from Rod Jenkins and Chad Weaver and if those guys think it's an acceptable practice then so do I! But if all your nocks are the same brand and style and some are loose and some aren't then I would just pinch them down a little or change out the ones that are too loose, and if they are secure on string as far as not falling off but maybe slip up and down then a second nocking point would fix that if you don't already have one, personally I ALWAYS have double nocking points to nock between, have seen it be a problem enough times I just don't even think about only having one. Good luck with it and if you think you might want to learn how to re-serve your string and maybe make your own strings, I think the DVD from Champion Custom Bowstrings is well worth the $20ish bucks it costs, had a bunch of good string hacks in it plus plans for making a string jig.