My 4* 40 manual isn't handy, but my 60 is. The four mounting screws are M4x22. That's 4mm in diameter and 22mm long. I bet they provide the same screws for the 40 size. Lowes has 4mm screws, and almost any auto parts or hardware store should have them also. Measure the remaining screw you have. It should measure .160" or about 5/32" if it's 4mm. If it's 22mm long, that will be about 7/8". You should be able to get Allen head 4mm screws at a larger hobby shop. That would be a step up from the Phillips head Sig gives you.