ietf-nntp Where did 497 come from for the max arg length?

[Stan O. Barber]

Overall line length is 512 (per RFC 977). Each line is terminated with CRLF,
that leaves
510. Each keyword and arguement is seperated by a space. So, a keyword followed
by a single
arguement is seperated by one space. That leaves 509.

RFC977 didn't set a max keyword length, but the longest one I could find in use
was 12
characters. So, the text says:

"Keywords MUST be at least three US-ASCII characters and MUST NOT exceed 12
US-ASCII characters."

509 - 12 = 497