Other than my power drill (drill motor) chucks, the chucks I use on my
machines are Jacobs, Rohm or Cushman, and require fairly common
standard keys.
There are keys that are interchangeable between numerous brands, but
any time I see keys at flea or garage sales, I usually get them.

For lathe owners, keys can be modified easily. Many chuck keys have a
removable T-handle pin, then the key body can be chucked in the lathe,
and the pilot pin can be modified/turned down, or removed. Those bent
L-shaped keys could probably be modified with a drill press.
Cut off the pilot pin and drill to fit a hard pin for the size of pilot
needed.
This might be an alternative to modifying the key holes in the chucks,
where the key pinion gear matches, but the pilot is different.

This method can also be used to replace those poor-fitting
auto-ejecting pilots on some keys.

The chuck ring gear/sleeve is somewhat adjustable on some chucks (if
only slightly). If a chuck was previously disassembled, the sleeve may
not have been pressed back to it's original location (changing the
distance from the ring gear to pilot hole).

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

Norm Dresner wrote:
I decided to get a new chuck key for my DP and, not knowing any better, went
to the Enco site. Well, I didn't buy my DP or its chuck from Enco so I
can't match any of their letter-sizes to what I have.

What is the normal method for specifying a chuck key size? Isn't it the
diameter of the pilot hole?

TIA
Norm