I think its a wrench to tighten the barrel nut on dan wesson revolvers, the barrel screws into the frame and the barrel cover then goes over the barrel and a the nut tightens the cover as the barrels are threaded on both ends.
Not knowing the dimensions of the opening it looks (guessing) like the wrench for the cap nut on a baitcasting fishing reel, with three different allen sizes for the breakdown of the reel.. As I said just guessing. Cheers