I think it might be. I have boxes of parts and every once in a while I try to make a pen. I took the clip off and threaded the brass bit so that it threads down into the body and the nose cone is threaded as well so a pretty solid pen.
I don't think it is the Zen as I tried one a while ago and I could not use it as a click style pen. Might even be the cone off of a Pilot Dr Grip as I think I had a bunch of these parts a while ago.