Polygon Corners are just designed to be cool looking and sturdy holders. I printed with 100% PLA. Doesn't matter what material you use, it is probably best to stick to 100%. The corners are good for thicknesses of up to 6.5mm. My guess is you shouldn't use it for thicknesses under 5mm or it will be wobbly. The screw hole itself is about 4mm.
If you like the design, but the sizing is off, and re-sizing on print just doesn't do it, ask me for a size in comments and I can make one that works for you.
-Print it the way I did for the best finish look. This way, the scuffs let by the support are on the inside and don't affect aesthetics.