I don't know where you'd find one that size. You may need to make one, and
CRS would probably be sufficient.
With an endmill, you could make a suitable key on your lathe, assuming that
you can mount the EM in a collet or even a 3-jaw chuck (not the best holder
but it'll work as long as it's done cautiously).

Grinding an existing square-ended key or other tool could be a simple
solution, as suggested earlier. An old 3/8" socket drive extension would be
good material for the key stem. You might not want to try drilling the
extension for the handle though if it's high grade steel. Welding a section
of round stock for a T handle on the end could work.

I've made a few keys from CRS and they're holding up well (I like a longer
stem for lathe chuck keys). For the endmill method, with a boring bar holder
mounted on the lathe compound, using a shop square will get the opposing
side cuts parallel.
The blending radius that someone mentioned makes a good looking finished
part.

A tool that I find useful is a 1/4" drive screwdriver-style handle with a
1/4" to 3/8" adapter on it, it's handy for quickly setting the independent
jaws on lathe chucks, then followed with the T handle type for jaw
tightening.

WB
................

"Harry Conover" wrote in message
om...
I recently purchased a used 4-jaw chuck for my Atlas 12" lathe.

The problem is that none of my chuck keys will fit it. The 3/8 is too
large, and the 5/16 marginally too small, so unless it's some *******
metric dimension, an 11/32" inch square chuck key would be perfect.
The problem is that I can't find any on eBay or even in the tool
catalogs.

The question is: "Does anyone know where a can purchase a 11/32"
square chuck key for a lathe 4-jaw chuck?

Thanks in advance.

Harry C.