Derivative of http://www.thingiverse.com/thing:7022When I printed out the original, everything worked OK (re-using the axis cap and all) but I was 3mm off somehow. Didn't feel like messing around with the STL so I made it again in openscad.The bolts are also a bit short, since they are supporting both this and the cap, but if you don't file down/drill out the holes more, they seem to actually support the bolts pretty well. If it comes off or starts to, I might change the design to have a countersink (I hope that's what it's called) for the nut to sit in - or you can just use longer bolts.Unscrew the top 2 screws on your y-axis cap closest to the idler, put this on the idler and put the screws in. Really, follow the directions from the original.