I think you could have a real problem getting the genuine bit for these.....however, its possible that another make would do, if the knob has simply an internal screw thread formed in it....personally I chuck these bits away and replace it with an ordinary nut and bolt - which does mean that you can't fold the handle up so easily. Most customers prefer that anyway! I reckon a good garden machine shop near you could sort things for you...plenty here in Hexham!
John
June 2009