From glass edge to glass edge mine is exact too. When I built my stand, I put a trim piece to cover the black edge so the opening had to be larger than that. That was probably your 1/8"
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,