I used one of these sandwiched between the stepper motor and the extruder. I did have to machine one of the bolt slots to match my x carriage bolt spacing though. Works fine on 2 of my machines.
http://www.amazon.com/Mounting-Bracket-Stepper-Geared-Printer/dp/B00Q6F51C0?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o07_s00