Hi everyone! I have a question. I am feeding a supply fan for make up air for a kitchen hood. My understanding is that NEC300.22(B) requires only 4' lengths in flex in this area. The hole is too small for the 1/2'' flex connector. So I tried a 3/8''90. No go! Do they make a 1/2'' or 3/8'' fitting with a 5/16'' head to fit this hole that is not threaded? Any help is greatly appreciated!!