knob for 1/4" hitch pins

thingiverse

if you have a hitch pin and want to convert the dangling ring to a solid knob. just pull out the ring, and tap the hole 6-32 thread. line the knob up over the hole so a 5/8" 6-32 socket head screw. the design in the picture converts a 1-3/4" pin into a 1-1/2" pin (from rim to the ball bearing).