2020 Cube M6 Corner

I am making an enclosure for my laser cutter. My 2020 is tapped for M6 not M5 and making the cube a few mm larger would be easier and stronger than making some kind of M6 to M5 adapter or waiting for more bolts to get delivered. (My hardware store is very lacking in metric bolts.)  Most of the cube corners I found were for M5 bolts or were not deep enough for my 4mm bolt head height to be flush enough for any bolts to get past making it useless. I used M6 x 20mm machine bolts.