vidicious @ScottElrod Thanks for asking. That is an earlier stylus with a slightly smaller diameter. The clip inner-diameter is slightly smaller than the stylus itself, and I used o-rings which fit quite tightly. I think the stylus is ~11mm (not on hand just now) and I know the o-rings are 3/8" (= 9.5mm).
I tried several at my local hardware store until I got the fit I wanted.