There are a selection of coupler sizes on ebay number 225144150240 Unfortunately I had to do a bit of work to widen the shaft diameter of the extractor but I used a piece of steel tube with a lengthwise split which the coupler fits over and tightens up using the fitted tightening bolt. For the drill end I just used a piece of steel rod - I think 10mm which was the maximum accepted by the drill chuck and fitted the coupler on it. The plastic claw coupler is pretty tight and I am considering filing it a little so it slips off more easily when you want to disconnect the drill from the shaft, Hope this helps. As I said I was told that a mains electric drill can burn out if you use one but the cordless seems to be fine and I use slow speed. If you want more info get in touch. Worth bearing in mind that I was quoted £600 for the correct motor and this fix was less than £10 for the coupler!!