Although described as a regular dies trial piece, these were actually deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J1480/P1633 with only 2 or 3 believed to exist, including the illustrated piece and one in StacksBowers 6/13 sale.
Aluminum J1481. Unlisted by Pollock as these have not been confirmed to exist.
Photo courtesy of R.M. Smythe from their July 2004 sale.