Although described as a regular dies trial piece in aluminum, these were actually deliberately struck for sale to collectors as part of complete sets.
Examples were struck as follows:
Copper J1187/P1327 with fewer than a half dozen believed to exist.
Photo courtesy of American Numismatic Rarities.
Aluminum J1188/P1328 with only 2 or 3 believed to exist including the illustrated piece below.
Photo courtesy of Heritage.