Granted Patent
Utility
US 5,129,311 · App. 07/554,060
Piston assembly with primary and co-centric secondary portions
Inventor:
R. Hart
Patented Case
View Patent ↗
Granted: Jul 14, 1992
Filed: Jul 16, 1990
Inventor
R. Hart
Assignee (at issue)
National Oilwell (U.K.) Limited
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.