022 switch controller screw size

[NarrowGaugeFan]

I have 022 automatic switches set up on a small postwar layout.  I'd like to fasten the switch controllers to a wooden panel without destroying the plastic molded sleeves that the screws fit in.  Can anyone tell me the proper size screw to use for this application?  

[cwburfle]

I've used long flat head 4-40 screws to mount the switch controllers to a piece of Luan plywood (nuts on the back).

[BigAl 956]

I use #8.