There seems to be an infinite variety of bushings of all kinds of different thicknesses. Comparatively, there is a much smaller set of tube sizes, 7mm, 8mm/O, 3/8", etc... However, bushings are made per pen kit. This seems backwards to me. I'm turning between centers with the excellent TBC adapters from bsnikitas and I'm using my calipers to measure fit about 30% of the time and rely on bushings when i know they are not worn down. What I would prefer is a set of TBC bushings that simply serve to fit the tube and provide the friction needed to turn the blank, yet do not correspond to any particular kit. Does such a thing exist? I tried searching the forum, but my google-fu isn't strong enough to find something so specific.