Granted Patent
Utility
US 4,445,456 · App. 06/273,699
Air filter restriction indicating device
Inventor:
Joseph Nelson
Patented Case
View Patent ↗
Granted: May 1, 1984
Filed: Jun 16, 1981
Inventor
Joseph Nelson
Assignee (at issue)
Engineered Products Company
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.