yep made these for my ctc i3:
locknut knob.JPG
fairly basic.
You just jam/glue the locknut in the middle. As there's no vertical stress on the knob, that works fine.
Think these use nuts for 3mm bolts. But easy to adjust in openscad:

// locking nut wheels
// wheel 20mm height 9mm
$fn=100;
nc=5; // number cutouts
nk=nc; // number knobs
difference(){
cylinder(d=20,h=5);


cylinder(d=6,h=9,$fn=6); // size of locking nut

for (i = [1:nc]) rotate([0,0,(360/nc)*i])translate([0,10,-0.5]) cylinder(d=8,h=10);

} // end diff

rotate([0,0,35]) for (i = [1:nk]) rotate([0,0,(360/nk)*i])translate([0,9,0]) cylinder(d=5,h=5);
Highlighted line line is the hexagonal hole for the nut. Measure max diameter of nut. Pointy bit to pointy bit. stick that in as the cylinder diameter. Easiest to adjust overall height in the slicer. just adjust z-axis (make sure to untick x and y axis first).