suffix for PGP exported key

I received a question about suffix for PGP exported key embedded in
PGP/MIME. RFC 2015 defines the application/pgp-keys content type but
doesn't define its recommended suffix, which is stored in
Content-Disposition.

It may not be a protocol issue but such recommendation is certainly
useful for Windows (and others) applications. Good examples are found
in the S/MIME spec.

Any comments?

--Kazu