Replacement O-Rings

you need these

I'm not sure of why, but often when I tighten the nose cone a little bit of the ring gets pinched and protrudes from the opening. I got these in case the o-ring gets damaged. This way, I don't have to sacrifice an o-ring from another pen.

they r o rings. specific for the pen.

O-rings

These were very handy. I haven't needed to replace any, but I used a couple to separate battery that I keep in a signal light. It's a long story, but the point is the product I used those o-rings for works as intended now.