E- ring size for Jucy 7 pad engagement adjustment wheel ??

E- ring size for Juicy 7 pad engagement adjustment wheel ??

I got rid of the @!#^%$ squeal on my rear brake ( I hope) by sanding my pads and doing the "crank and tighten" procedure.I just got back from a 1/2 hr of braking every 20' or so and no problem (I hope)

I quess that due to the light sanding and rebedding I did to the pads, I had to reset the pad adjustment wheel, but when I tried, it just popped out of the handle. The e-ring/split ring retainer for the bottom of the knob screw is missing. Anyone know what size I need short of pulling out the knob again and walking into the hardware store ?