i made some of these and didnt have any nocks break. my local walmarts didnt have the thill nite brite replacement lites but dicks sporting goods has them in new jersey. i didnt see any difference in where my arrows hit. i made one for all my buddys too. the only thing different i do is pull the light out of the nock and flip it over and stick it back in the nock when i turn the light off. if you dont make sure the hole you drill is cleaned out good and burr free they can stick inside the nock and i have ruined 2 of the lights so now i make sure the holes are cleaned out and i just flip the light when im not using the nock.