Brent
That brass piece pressed onto the tuner is actually a vulcanized rubber water lubricated bearing that is used in propellar shafts in boats. The generic name for it is a "Cutless" bearing. Google that and you will see.
The brass shell is simply what holds the shape of the rubber. I actually turn the brass shell down to where it is only about .050 wall thickness. Using the rubber is one of my own ideas, it acts like a "snubber" on the barrel. By that, I mean it actually dampens vibration.
My first tuner did not have the snubber, I added it on a whim, and I believe it broadens the load window. I do not have any scientific data to back that up, I just go on the way my Rifles perform. The tuner actually weighs about 5.5 ounces.
Those rubber bearings come in sizes from 3/4 inch ID all the way up to 48 inches ID. (that's pretty darned big). The one I use is for a 1 1/8 shaft. It is pressed onto the tuner body with about .020 inch interference fit. The rubber grips the aluminum tuner body very tight.......jackie
