Greetings Douglais, and welcome aboard.
Skeet Master and Claude Purbough come to mind when thinking of old school sub-gauge barrel inserts. They allowed the shooter to use 4 gauges in one gun. These tubes required the replacement of the extractors each time the tubes were changed. More than once I witnessed an unhappy shooter who'd dropped an extractor during a tube change. I haven't seen any of these tubes in about 20-years. The last two sets I saw were fitted to a FN Browning and a Remington 3200. The newer captive extractor tubes, made popular by Jess Briley, pretty much put an end these tube. There's nothing wrong with the way the older tubes shoot, they are just a bit more of a bother to change.
Doug, the tubes your have are period appropriate to your Superposed and were probably once owned by a competitive Skeet shooter. You have 3 sets of tubes with extractors and the installation and removal tools. Typically, the tubes were individually fitted to a specific barrel. So, you'll want to keep them with the gun. I have several guns fitted with Briley tubes and they are numbered to match the gun and marked top and bottom so they will be used in the correct barrel. You may wish to check your tubes for identifying marks. The object of tubes is to have the same handling in the four gauges competed in NSSA Skeet. Many shooters would add a barrel weight when shooting 12-ga so the gun would have the same swing dynamics with the tubes removed.
