This ruler square was designed for a 1.00mm x 28.50mm steel ruler. I've provided the CAD (Fusion) file (and Step file) so that it can be modified for other size rules. It uses a heat-set, 5mm brass threaded insert and a 5mm brass thumbscrew from Amazon. There is also an optional printed "shim" which you can use that fits into a slot so that the brass screw never contacts the steel rule directly (this is already in the same CAD file). I used PLA with good success. I found that when I used "auto place" on Bambu Studio, it rotated the part slightly on the bed, and this gave a much more accurate slot for the rule. In my case, it was a perfect snug fit without being too tight or loose.