The thread size is 8X40. You probably wont find them at your hardware store, I tried as well
Another thing to watch out for is with non-factory screws you might get some that are not as hard as the ones that TC uses. I bought a set from ebay that I cut down myself and they bend everytime I shoot
I called TC today and they had never heard of that happening. They are sending me a set to try out. Just something to think about