I"ve been trying to find an answer to this question myself and belive the Autolite 3924 corresponds to the Champion RC12YC.24-7423 - Champion RC12YC Spark PlugRC12YC Champion Replaces Autolite 3924, NGK BCPR6ES..
I have autolite sparks plugs ARF32M and need to know the cross reference to NGK
Most all brand spark plug brands are on the cross reference including Champion. Some of the brands that cross reference to Champion are Autolite and Denso,
champion #940
Champion RA8HC has the same thread, seat, reach, hex size, and terminal type. I ordered a Kohler plug from Amazon and they actually shipped me this Champion Plug.
Champion
rj19lm
cross reference ngk BP4HS
It crosses to a champion stock number 405.
NO.
NGK BP7ES, Bosch W7DC, Champion N9YC
Champion 5861 or Autolite 458.