Basically just a clamp on the barrel fiber optic made by HiViz (I think, maybe TruGlo).  Snaps on to the rear of the bead.  It's a nice bright dot.  Only problem is when shooting a class recently, I was shooting a round of slugs at 25 yards, I found it to shoot about 2" high.  After further looking I realized it was half a bead lower then the factory installed bead.  So it made me shoot a touch high.  With buck shot, and really slugs too, it's not a huge deal.  But something to mention.  You want it? Come get it.  I don't think I put it back on.  I think I'll be drilling out the silver bead, and tapping it for a screw in replacement.  I'll be doing the same with the black one too.