Granted Patent
Utility
US 4,369,728 · App. 06/232,422
Air filter restriction indicating device
Inventor:
Joseph Nelson
Patented Case
View Patent ↗
Granted: Jan 25, 1983
Filed: Feb 9, 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.