Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:1443598.
UPDATE 20161005: I have since upgraded to this: http://www.thingiverse.com/thing:1635585
I was not happy with the official Wanhao clip that keeps getting looser and looser as you use it, and I did not want to drill holes in the gantry, so I designed my own.
It is a very tight fit, it has to be. I iterated the design a few times to make it work exactly right with my printer, which is a 1st gen Wanhao i3 Duplicator, but you may have to modify it to fit yours. The model is on Tinkercad. Edit it here