Jim I do not know the difference but I have a couple of the 85 TSS trap sets including the unsingle, one for me and one set for my wife. I bought the sets for about $1,800 for each set used from people on Trapshooters. There is no better value for the money if you want an unsingle adjustable rib gun. They are solid and well constructed and shoot like crazy. I used the double yesterday as my back up gun.