I believe the suggestions of metal thread inserts, and blind nuts are a good answer to the question of having thread strength. Helicoil inserts do work as long as the dowel insert used to replace the oversized drilled hole. Keep in mind that the helicoil continues to try expanding with could crack out the installed dowel insert if the wall thickness is thin. I have been lucky in tapping threads in hard wood blocks, and using thin CA to harden the threads. A new tap does cut better threads.

aerorich73