KF flange - Small ISO flanges; originally Klein Flange developed in Germany, "klein" meaning small; Kwik-Flange™ is the MDC trademark name for the smaller components of a complete ISO flange family.

DN - Diamétre Nominal (French); nominal diameter, usually referring to vacuum tubing internal diameter

NW - Nenn Weite (German); nominal diameter, usually referring to vacuum tubing internal diameter

Please find the followings.

http://www.mdcvacuum.com/searchs/doc/kwik-flange-kf-intro.htm
http://www.5pascal.it/pdf/5PA-701-880-C_flange_fittings_2006.pdf
ISO 2861
ISO 3699
ISO 1609