When the United Kingdom was considering adding a decimal coin denomination in 1981, samples, or trials, of a seven-sided 25-pence coin were produced by the Royal Mint. The coin was needed to fill the gap between the 10- and 50-pence denominations.

An example of the trial piece is offered in Dix Noonan Webb's April 2 and 3 auction in London.

When the new denomination was under consideration, the 25-pence denomination was used only for commemorative designs and was a rather large, unwieldy size.

Treasury opted to add, instead, a seven-sided 20-pence coin, and the 25-pence trial pieces were consigned to the dustbin of history. Though copper-nickel examples are known, Dix Noonan Webb reports that no specimens have previously been recorded in nickel-brass.

The example in the auction is “as struck” and is estimated to realize £600 to £800 (about $990 to $1,357 U.S.).

To find out more about the auction, or the lot, telephone the firm at (011) 44 20 7016 1700, email it at auctions@dnw.co.uk or visit its website, www.dnw.co.uk.