It does look like typical coffin hardware from the second half of the 19th century: a thumbscrew that most likely would have been inserted into an escutcheon plate--the escutcheon may have had matching design elements.  But is there any other evidence of coffin burials in this mass grave?  Nails?  Any other hardware? Tacks, with white metal or cu alloy heads?  

Check out the following publications to get an overview of coffin hardware--and also James Davidson's recent work.  There are also many coffin hardware catalogues out there which can narrow your date range substantially. 

Laurie


Bell, Edward
1990	The Historical Archaeology of Mortuary Behavior: Coffin Hardware from Uxbridge, Massachusetts.  Historical Archaeology 24(3):54-78.  

Garrow, Patrick
1987	A Preliminary Seriation of Coffin Hardware Forms in Nineteenth and Twentieth Century Georgia.  Early Georgia 15(1-2):19-45.

Hacker-Norton, Debi and Michael Trinkley 
1984	Remember Man Thou Art Dust: Coffin Hardware of the Twentieth Century.  Research Series 2. Chicora Foundation, Inc., Columbia, South Carolina.

Kogon, Stephen L. and Robert G. Mayer
1995	Analyses of Coffin Hardware from Unmarked Burials Former Wesleyan Methodist Church, Weston, Ontario.  North American Archaeologist 16(2):133-162.

Little, Barbara, Kim M. Lanphear and Douglas W. Owsley
1992	Mortuary Display and Status in a Nineteenth-Century Anglo-American Cemetery in Manassas, Virginia.  American Antiquity, 57(3):397-418.

Laurie Burgess
Associate Chair
Department of Anthropology
National Museum of Natural History
Smithsonian Institution
MRC 112
P.O. Box 37012
10th and Constitution Avenue NW
Washington, DC 20013-7012
(202) 633-1915
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