The installation screw could be a number of types, so the best I can do is give you a ballpark range. It could be a self tapping flat head screw, of which we carry two; either a 33-016 #8 x 1", or a 33-079 #10 x 1". However it may also be a machine screw that is #10-24 x 3/4" long. It's hard to say for sure without knowing the length of the original screws, but give these a look.
