I believe it was 5-10 years since I last replaced the bunks on my trailer. While I have a drawing that I used to measure them up for the next replacement, I forgot to get measurements for the holes off the last set so that I can go the carriage bolt route for the next time. I guess it is time to check the carriage bolt tightness the next time that I launch the boat or get bored at home and feel like climbing under the trailer.