HI JACKSON JR! Depends whether or not your firewall is made out of aircraft ply or cheap ARF junk. If it is good wood, then wood screws will work on your smaller [.25 and under] engines. the threads that you form in the wood should be hardened with thin CA glue. If you aren't sure about the wood, you can "fish" blind nuts into drilled holes by sliding a long wire into the fuselage through the firewall, slide the blind nut over the wire, then bend the end of the wire into a tight T. then yank the wire to seat the blind nut. You should start a bolt into the nut carefully, and tighten it to fully seat the nut.