Want the reasoning for them or just a short answer?
Heck, I feel pretty good.
If you take a tube like a mag tube and slide another tube over it like a slide tube, you get friction, you get binding, you get wear marks etc etc etc. Over the years, gunmakers have tried diff things and methods to eliminate those probs. Use a looser slide tube? Cuts the friction but you get more binding and wear marking in looser parts. Sloppier fit, too.
Those things on that tube above were called bearing rings and were one of the more common fixes for slide probs. They cut the friction of tube on tube contact by cutting the total area where the two tubes touch down to just the surface area of those bearings. They cut wear marking by keeping the two tubes off each other and the only marks you would get were on the hidden bearings. They cut binding by keeping the slide tube aligned with the mag tube.
Other ideas used over the years included wrapping the mag tube with a coiled wire spring like a mag tube spring, just on the outside of the tube....leather/plastic/nylon/teflon contact pads/bearings glued to the inside of the slide tube....split ring bearings on the slide tube ends and slide tube nut....pressed dimples in the slide tube....slots cut into the slide tube to cut steel on steel contact....heck, the Mav 88 even eliminates the steel slide tube altogether and uses a slotted synthetic tube. You have to have some method of tube to tube contact that will cut the probs....so it's either a straight tube slide tube with mag tube addons or a straight tube mag tube with slide tube addons.
Those ring bearings like above work just fine by themselves....therre's no point to dropping them just for nothing. The only prob you'll run into is if you need to switch mag tubes or slide tubes. You'll need to match the proper slide tube to the right mag tube or they don't work. That above tube will work with an old style straight slide tube, no bearings or dimples. If you use a current dimpled slide tube, it won't work with ring bearing tubes so you'll need to replace the tube, too.
All Mossy tubes and slides can be interchanged, though. I mean as in just buying a new mag tube and slide and switching out those old parts for new ones. Just switch both tubes at once as a unit.
That all you needed to know?
rich
