I recently bought this chuck, a product of Inner Mongolia,
http://littlemachineshop.com/product...ProductID=2276

and the snug-fitting 5C mount LMS doesn't list as a backplate for it.
http://littlemachineshop.com/product...ProductID=5479

5C isn't just convenient, it allows the chuck and work to move between
the lathe and an indexing fixture on the mill. There's another
tool-grinding version of the chuck, lacking the outer steps, that some
people report receiving instead.

I now understand the advice that 6-jaws aren't the best
general-purpose chucks and am glad I didn't spend several times more
for the larger choices. It does grip difficult parts like hex bolt
heads and tubing better than a 3-jaw but it isn't a good substitute
for collets for accurate work. The internal gripping range is 0.2" to
about 1.6". The external range is about 1.3" to 3.9" on the steps, 5"
on the unground jaw ends if you don't need the steps to square up the
work.

It won't be my choice for heavy cuts, especially with the jaws opened
wide and little scroll engagement.

--jsw