I was going through some stuff and came across these plans. They were drawn by Robert Coyle who originally designed the thing. I think it was back in the late '80's that I saw him at a small Arizona convention. He had one of these that he was carrying around the show. We got to talking and he kind enough to draw up some plans for me.
I will point out that the tip in this image below is how it appeared in the movie(as I understand it) and as you can see it is extended more. The 3 prong M16 tip as it appears above is as it was originally conceived....so take your pick. Also note in the image below the little box showing the fin detail. In the film the recessed edges were at an angle.
On the communicator and ST3 pistol disruptor you may recall the half spheres which I have always heard were explained as batteries. Robert told me he originally designed the rod on the bottom to have a ball on the end to sort of keep with the look the other props.
So there you are. The increments are in inches and it is a simpler shape so it should be a fun project for those who have the iniative.
I used to have number 8 of these made and images of that piece are on the web.