The design is the same as the original by blacky, i just redesigned in sketchup reducing the nut and washer hole and simplify the mesh for a better print.My nut measures 8mm external diameter, and 3mm height. The washer is 9mm diameter and 1mm height.I printed mine with PLA, .35 nozzle, .25 layer height and works good but if you want more strength reduce the layer h to .20. I sliced it with Slic3rJust print, put the nut and the washer! :)