The sleeve itself is an air-bump can... i have used them to mount my the shafts i made for the timbrens. The air bumps are about $200 a piece while i made my bumps for about $23 each and some scrap steel.
Here is a shot of an airbump in the cans...
Yes the can makes it adjustable up and down, but some say that you can't tighten the can enough to hold the bumps on a hard hit bottoming out. So, usually they are designed to be used right at the bottom where i ahve them, with some kind of retaining ring on them.
Make sense?