The best UK coin ever. Brass-coloured, with twelve sides, and thick, with a picture of thrift on the back.
Let me take you back in time. Back to before cellphones; back to before the microprocessor; back almost to when Neil Armstrong set foot on the moon. Way, way back.
In 1970, the Brits still spent pounds in the shops, but each pound sterling was divided into 20 shillings and each shilling was divided into 12 pennies. In 1971 we changed to the metric system, and re-defined the penny so that each pound contained 100 of these new pence.
But when I was a schoolboy, we had florins and tanners and half-crowns. Each week my mum would give me a huge half-crown coin to buy my school dinners for the week.
The farthing had gone out of circulation, but we still had the ha'penny (or half penny). We had pennies; great, round weights that could buy a real penny-chew. We had silver sixpences: tiny coins, found in the Christmas pudding.
In the middle of all these beautiful coins was the threepenny bit, or "thrupny bit", if you were talking. The ugly duckling of the 1960s British monetary system.
The threepenny pieces that I spent in the sweet shop on the way home from school had 12 sides. They were much thicker than a penny, almost as thick as a modern £1 coin, and roughly the same size. In fact, they were a similar colour to the modern £1 coin, but quite different, because of those 12 sides.
The real dimensions of the 3d coin (that's d for denarius) are 21mm across (from flat to flat) and 2.5mm thick. The weight was a nominal 6.8 grammes. The alloy is a copper-rich nickel-brass (79 percent copper, 20 percent zinc and 1 percent nickel).
For comparison, a modern £1 coin is round, 22.5mm in diameter, 3.15 mm thick and weighs 9.50 grammes. It is also made from a nickel-brass alloy, but is has less copper and more nickel (70 percent copper, 5.5 percent nickel, 24.5 percent zinc). The nickel keeps the modern coin bright and shiny, while the copper gives it colour.
In summmary, then, the 3d piece is a bit lighter and thinner and appears a duller, deeper yellow colour than the pound coin.
History
This strange coin was introduced in 1937, to replace the too-small silver threepence. It was withdrawn from circulation with decimalisation in 1971, but all coins minted after 1967 bear the 1967 date. Apart from the end of the 1960s, the coin was minted every year except 1947, though few were minted in 1946 and 1949, and these dates have a relatively high value. Upwards of £100 each for mint-condition examples.
As with all British coins, the obverse shows the head of the monarch, while the design on the reverse changed over the years. I remember two designs; the portcullis (See here for a pic), and one showing a strange plant, that I recently discovered to be thrift (see here for a pic). It so happens that in years leading up to the 1939-45 war, the government was encouraging a different sort of thrift. Perhaps someone in the Royal Mint was having a quiet joke at the government's policies.
The thrift plant was used from the introduction of the coin in 1937 up to 1952, when the portcullis came in. Perhaps the government policies changed around the same time, I don't know.
Value
A threepenny bit was worth threepence. Four of them made a shilling, so each was worth fractionally more than a modern 1p. That's about two eurocents in modern parlance. At the time, it could buy an ice cream, or three penny chews. Or some Liquorice Allsorts, or gobstoppers.
Trivia
Oddly, perhaps, the threepenny bit could roll, albeit noisily. The corners were just a little bit rounded, and the angles between each of the sides were obtuse enough that the little things would roll along a table quite happily.
There's a phrase in engineering parlance -- maybe motoring parlance as well-- which refers to the dodecagonal shape. When a circular wheel skids along the ground, or along the rail, sometimes part of the circumference is worn flat. The bumpy ride caused by this flat spot on the wheel is called "threepenny bitting". The same applies when there is a characteristic stick-slip action to a motion that should be smooth and circular.
I still have 18 of these things, dated 1938, 1939, 1940, 1941, 1942, 1943 (twice), 1945, 1950, 1952 (all with thrift) and 1954, 1955, 1956, 1957, 1958, 1960, 1961 and 1967, with the portcullis. None of them is in any better than "good" condition. To a coin collector, that means they are all but worthless.