How to remove "Knob Handle -Locking (part#131-0897) from new Toro model 20355

This is for a new Toro model 20355. The Knob Handle (part #131-0897) which is supposed to hold the propulsion cables to the mower handle turns counter clockwise to loosen the cables so they can be pulled upwards to increase propulsion responsiveness. There are two cables on this model - one for forward propulsion to the rear wheels and one for backwards propulsion to the front wheels. When I tried to loosen the knob handle it would turn fairly hard and hit resistance about every half inch or so. I could not tighten it more either by trying to turn it clockwise.  I suspect it is stripped in some way as turning it counter clockwise which should loosen the cables does not loosen them at all.  it just hops over all these resistance areas. 
 
I thought buying the parts (a Knob Handle - Locking 131-0897 and the Screw-Carr 3229-8) would be far cheaper and faster despite warranty at $5 for these two parts than driving for a couple hours and then having to go back to get it later at a Toro dealer.  But I have no sure idea how it actually works to remove it to be able to install a new one other than to break it off. There are only 5 parts to the whole apparatus as in the attached photo and this one on this model is slightly different than others on other models. It appears the knob and screw are the only working parts one this apparatus as the other 3 parts are primarily there to hold the cables tightly to the mower handle. The knob just seems to tighten and loosen on the screw that comes through the handle from the other side.  in fact, I am wondering if I should replace it with the Toro All Wheel Drive model version since it has two cables for front and back wheels also. 
 
So I am wondering how to remove it. Can anyone help with this? There is no simple nut on the knob end to remove off the screw (really a bolt though they call it a screw) has no screw driver slot to turn from that side to remove it.  While I could not get it to work I suspect the knob handle is made to only loosen so far and not come off the screw yet still tighten to hold the cables tight to the handle. 
 
Many thanks!