Design of this stamp is a mail airplane radiator with propeller attached.

This is part of the second air mail stamp series, primarily for use on the new
air mail service between New York and San Francisco. Three air mail zones were
established: New York to Chicago, Chicago to Cheyenne, and Cheyenne to San
Francisco.

The rate of postage was eight cents an ounce for each zone.

These stamps were sold at the Philatelic Agency in Washington, DC, before they
were issued to postmaster.