I designed these for 10 series aluminum extrusions that are 1" x 1" square. key differences over others of the same, the nut is twisted to grab mor metal when tightened, and the corners are rounded for easier printing. Long version: As most know t-nuts are expensive $9 US for 25 and then $15 shipping which is outrageous so I used M5 nuts and bolts, I probably should have tried M6 but I couldn't find any at the hardware store and didn't want to buy 200 of something that I had to grind the edges off, all I could get at the hardware stores was 1/4" (grind it), M8 (way to big) and #8 screws (too small) so I went with something that I knew would grab but didn't need to be ground but they are too small to touch the sides and so would spin and would flop around in the channel so I printed some holders for the nuts, there were quite a few out there already but they all have the flats of the nuts parallel to the flats of the channel and they don't overlap that much so I could see over tightening the screws and it pulling out of the channel so I made some that the nut is turned so that it grabs as much of the channel as possible, I also rounded the edges for several reasons: Update 8/27/2015: I needed some holders with the nut closer to the edge to get in close to the corner of a printer I am making, I shortened just one side of the holder and included it as well and it is also in the sketchup file. I printed them with ABS, not for any real reason other than I had a lot of out of spec ABS that I had unwittingly bought until I found a good brand. 0.4mm nozzle 0.2mm layer height 15% infill 240c hotend 110c bed ABS juice to hold it down. ;-)