Curious what you've been told about, or for instructors what you teach about tenon diameter. I start beginners and new bowl turners with the guidance that the jaws should be "close to a circle" with just a little space between them. Realizing, of course, that for a small bowl the tenon diameter (hence the jaw gap) can be bigger. A colleague today challenged the axiom a bit, saying the the way the profile jaws on,.say, a Talon or Stronghold chuck are shaped, the contact points need not be all that close together. Even mentioned a chart that gives bowl size and recommended tenon size. Is there some other rule of thumb that I can/should offer to the novices?