Does anyone know what size screw this is for Diana 34

Call Mike Melick at Flying Dragon Air Rifles. He will know the size and probably has a replacement. Phone # is 515-924-3699. He's also a great guy to get to know. He has helped me several times. Call before noon Central Time. He's in Iowa.

Dint remember off the top of my head, but I believe they are a 5 or 6 mm metric thread. I always replaced mine with allen head screws to eliminate buggered up screws. They are metric for sure!!

It’s a M6-40. Crow Get some M4-10 scope mounts.