I am thinking about buying a few of these jigs
but I have a question-the ads say self centering regarding the shafts.
Now if I want to fletch different dia shafts,do I just adjust the knobs to put lines directly over both C marks and that will be top dead center  for any shaft diameter? and then adjust for offset or helical?

I fletch 5/16, 11/32 and 23/64 shafts on my bitzes with out changing the settings. I have my jigs set for maximum helical and the feather makes good contact with the shaft no matter what size I use.

I also fletch all my cane with a blitz and have no problem at all with different size shafts and the feathers lay down on the shaft great.  I also have a nock indexer on one of my blitz that lets me index each nock for orientation. Wishe they were still made.

I fletch all diameters with my Bitz,its a great well made solid jig.

Switched from a jojan a few years back-BIG difference!  Bitz always contacts the shaft!

I've never changed a thing form 5/16" carbon to 23/64 wood

Bitz is Da Bomb!

You Cannot Go Wrong with a Bitzenburger Fletcher!! Not Propaganda, I wish I had a Couple More of them myself!!
 Easy to set-up, and after you get what you want, Never, generally, have to Touch them again!!  
  Money Well Spent, and My GrandChildren will Use it Long after I have Expired!!