Well, hopefully, you did not try and screw sheet metal screws into machine thread holes, or, if you did, you stopped before you boogered up the threads. Now, go to your local hardware store and buy one each of the smaller size bolts, say 6/32, 8/32, etc., bring them home, and try them to see what fits. Then you know what the thread size is. Length? Get a couple of sizes and see which one does the job.
Maybe someone else will know the size and save you the trouble. I have lots of different sizes in my shop so it is easy to do. Beseler will be US not metric and that saves you lots of trial and error in finding out what you need.