You have a “master ring” cylinder cylinder patented (#414,720) by Edward O’Keefe, a New York City locksmith, on Nov. 12, 1889. Those cylinders have a concentric ring surrounding the plug creating two shear lines. The plug shear line is used for change key operation while the ring shear line is for master keys. On large master key systems, this prevents the key interchange problem common to conventional cylinders using “split-pin” master keying. The system has fallen out of favor due to the development of higher security key systems and the fact that some contemporary hardware won’t accommodate the larger diameter cylinders. They are still made for replacement purposes however. Your cylinders are for key-in-knob locksets although they are also made in mortise and rim formats. For more information, scroll down to page 19 of the Corbin Russwin Key Systems pdf at the link:
http://www.gmslock.com/category.php/7/IC-Cores
Pete Schifferli
