kody here again, answering my own question for anyone interested. The advertising done by all of the dealers handling the Burris products pertaining ,at least to this range of red dot sights is horribly and needlessly confusing. #1 Burris makes and has made 3 different red dot reflector sights , the Fastfire Mark l ,Mk ll and Mk lll. They were developed in that order ,with ongoing improvements ,as reflected by their costs. [Read all the ads closely] The latest ,the Mlll comes in two versions with different P/Ns ,3 moa reticule and 8 moa. The previous mods had similar options and one of them had a 4 moa reticule. The M lll has the battery replacement cover where you can access it! The Speedbead is the base designed for a specific gun. It will mount the Fastfire of your choice. In my case it was specifically for the Benelli M1 Super 90. I think most people could make any of the Benelli Mods fit on any of thse guns. Basically they are just a standard base catilevered back over the frame/stock division and attached to a round flat plate that fits like a pitch adjustment shim ,between the stock and the frame. Other guns require a Weaver /Picatinney base for the receiver, or whatever works for another type gun. Ther is more info that I can't describe offhand so If I can help, PM me. kody