The arm rest width adjustment of my modular pull apart mobility scooter is achieved by loosening one or two plastic knobs that cover a bolt thread. It turns out the original ones are really fragile, I've attached photos of the better one of the two.
With the first pic the three strengthening ribs are all damaged to an extent. One has broken completely, one has a split and the other is bent. The 2nd shot shows the part that's gripped by the hand ti make the adjustment.
I paid a visit to the local hardware shop today and bought a pair of more durable hand knobs, one is shown in the 3rd pic.
