I have one "non-adjustable" 3-jaw chuck in the shop I use on my 9" SBL. All my other 3-jaw chucks are either Adjuster-True or Set-True chucks. On the non-adjustable chuck as I call it, I purposely turned the boss about .005-.007" smaller than the register on the chuck. Doing this allows me to "bump it" around as George mentioned above to get the work piece running true. One thing to remember, as the chuck gets used, you will notice some runout in a couple of thousandths on different diameters as you use it. So what do you do? On mine, I loosen the screws so they are snugged, then start bumping the chuck around until it is running true, then tighten down the screws. They don't need to be hammer tight, tight enough with a long allen wrench. With a chuck tight against the back plate register, you don't have that option of adjustment. Ken