Granted Patent
Utility
US 4,228,669 · App. 05/921,442
Double cylinder lock with key retention
Inventor:
Daniel Bischoff
Patented Case
View Patent ↗
Granted: Oct 21, 1980
Filed: Jul 3, 1978
Inventor
Daniel Bischoff
Assignee (at issue)
KYSOR INDUSTRIAL CORPORATION
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.