Use any #4-sized screw or nut/bolt for assembly, but we use special #4x1/2" screw designed for threading plastic to mount these to our chassis. This screw also does a great job going into the steel bracket!

Note: We've discovered our latest batch of GM2 motors were molded a wee bit fatter around the tab that the motor-retainer screws into. This interferes with the little side-notches when you install it, so you have make the side-notches a wee bit deeper with a file. Or if you're feeling dangerous, you can use a small drill bit and "ride" it down into the notch a bit. Of course this is totally the wrong way to use a drill bit, but sometimes you got to use the tools you have!