Pen Cap...

Just some random pen caps.
And they also work on the NotAPen...
The Standard is just that, a regular old TiBolt cap.
Attach a lanyard to your pen, with The D.
Mounts either in line with your pocket clip, OR perpendicular to it.
Your choice when you install it!
Need to bust a window?
Put one of the BallBreakers on the end of your pen, and give it a whack!