The What's It committee tries to identify unknown items. Here are some items that have been identified by the patent dates on them.
Stretcher Frame Example marked PAT.D Feb 13 1883 JUN 16 1885 A. D. S. Patents 272,162 and 320,300
Nail Set US Patent: 512,119 Article in the March 2009 Gristmill. Example is 1/4 inch thick, 1 1/4 inches wide and 4 3/8 inches long. It's only marked PAT'D JAN 2, 1894
Also from the March 2009 Gristmill: Hose Carrying Tongs marked only PAT APLD FOR. Identified as patent 763,338
Here is an item received from the internet that was identified as a barrel making tool: Hoop Lock Cutter. Picture and sketch from a catalog shown.