James Waldby wrote:

Although one can use a hex key (Allen wrench) while it's attached
to a ring, it only takes a moment to remove the key from the ring,
for more-convenient use.

Pull on the key while turning it as if unwinding the spring that
holds it, and it will come right off. To put it back on the ring,
push on it while turning the same direction.

I used to do this, but found that after I'd removed and replaced the
keys I use most often a few times, the spring connection to the ring
broke. The spring which fits around the key is pretty tight on the CK sets.

Chris