Parametric Y carriage for RepRap prusa mendel i2 i3 http://www.thingiverse.com/thing:449055 Edited to fit aluminium bracket, plus I added M3 nut .... things that you zip-tie to all 4 corners of the aluminium bed to keep the nut from moving when leveling the bed.Place on the aluminium bracket with the screw-hole aligned and drill the remaining holes where you need them. Before you mount the bracket zip-tie the 4 holders to each corner (you can just about see them in the last photo). I also added a bit of superglue around the nut to keep it firmly in place.