I may be mistaken, but I recognize them as seats at one time sold by Archer Seating, who removed like all of the Seats from old Baltimore Memorial.
Here is a 2007 auction from Huggins/Scott. Scroll to the second to last pic and click to enlarge and you get a detailed view of a single.
http://oct07.hugginsandscott.com/cgi...pl?itemid=6916