Uniformity of specification within the sterling area.Before decimalisation, the specifications of the coins in one part of the sterling area did not always match those of their counterparts in other parts of the sterling area. For instance, the Irish threepence was small, round and thick and in cupro-nickel, whilst the Guernsey threepence was small and scalloped and also in cupro-nickel, whereas the UK threepence was small, thick and twelve-sided but made of nickel-brass. It seemed that the smaller the denomination, the smaller the likelihood of uniform specifications throughout the sterling area. Going further afield and further back in time, a lot of the pennies and halfpennies in the British Empire had a central hole (Fiji, New Guinea, British West Africa, etc.).
After decimalisation, however, all the coins of the remaining sterling area matched their denominational counterparts in size, weight, shape and colour. I say "colour", because it is likely that pound coin changed its metal content at various times in various places, while still remaining a brassy colour. The one denomination in which we do see minor variations, though none that would be detected by a vending machine, is the twenty pence. This coin was first issued in the UK in 1982, and in addition to its heptagonal shape, it was also countersunk. making it look even more distinctive. However, not all the twenty pence versions of the sterling area are or were countersunk.

UK twenty pence, first issued in 1982: countersunk surface.

Jersey twenty pence, first issued in 1982: flat surface.

Guernsey twenty pence, first issued in 1982: flat surface.

Falkland Islands twenty pence, first issued in 1982: flat surface.

St. Helena and Ascension twenty pence, first issued in 1998: countersunk surface.
P.S. I am not to blame for the labelling of the image. "FRONT" and "BACK" (!) are reversed, of course.

Left: Gibraltar twenty pence, first issued in 1988: countersunk surface.
Right: Gibraltar twenty pence, first issued in 2004: countersunk surface - but notice that the rim is wider than in the previous version.

Isle of Man twenty pence, first issued in 1982: flat surface.

Left: Isle of Man twenty pence, 1992: flat surface. Right: Isle of Man twenty pence, 1993: countersunk surface.
From 1993 onward, all the Manx twenty pence coins had a countersunk surface. The Isle of Man is the only part of the sterling area to have switched the surface type of its twenty pence coins.


The 20 pence of the Isle of Man's new design series of 2017 is countersunk on the obverse but flat on the reverse - another Isle of Man first!