This famous piece is a 1795 draped bust silver dollar from dies not known to be used on any regular issue silver pieces. It is struck on a 96 grain copper planchet (per PCGS) with the diameter of a Large Cent, and is from dramatically rotated dies.
The piece is unique and is ex Woodward 4/1863, Parmelee (New York Coin & Stamp 6/1890), Woodside (New York Coin & Stamp 4/1892), Woodin-1914 ANS, Newcomer, Boyd, Kosoff 7/1951 Numismatic Gallery Monthly, Kosoff 5/1955, Hydeman-Kosoff 3/1961, Stacks 5/1975, private collection, Lustig, Byers, private collection. It is graded PCGSAU55.
Various explanations for the coinís existence have been proposed. Adams and Woodin listed it as AW18 and called it a die trial piece. Judd listed it as a mint error. (Now under review.) Stack's called it a "setup trial piece to insure (sic) the striking distance between the obverse and reverse dies" in their 5/75 sale. (Saul Teichman disagrees because it is not as thick as a dollar planchet. He also notes that the Mint was able to create full size dollar planchets in copper for the 2 1794 dollars J18/P27 and J19/P28, and that all other die trials of this year are full-sized as well). Andy Lustig argues that it is either a die trial on an undersized planchet, a die trial on a full size copper planchet that was later cut down for use as a large cent planchet, or (most likely) a mint sport that could have been struck anytime from 1795 to 1863.
Photos courtesy of PCGS.