British West Africa, 1939 AD., George VI, King's Norton mint, 3 Pence, KM 21.

British West Africa, George VI, engraver: Percy Metcalfe (obverse), 1939 AD.,
3 Pence (21,5 mm / 5,09 g), copper-nickel, mintage 15.500.000 , security edge,
Obv.: GEORGIVS VI - D· G· BRITT· OMN· REX· F· D· IND· IMP: , crowned head of George VI facing left.
Rev.: BRITISH WEST AFRICA / 3 / PENCE / 1939 , value and denomination in wreath, year below.
KM 21 .

from http://www.wbcc.fsnet.co.uk/sub008a.htm : The “King's Norton Metal Company” (King's Norton being an area south of central Birmingham) was another private mint in the Birmingham area. One of its first important contracts in the coinage business was a contract to supply blanks for British farthings, halfpennies and pennies in 1911 and 1912. During the following ten years the mint fulfilled a number of contracts for coinage. These earlier contracts were for coins for places such as Great Britain, British West Africa, East Africa and Egypt. The mint’s “KN” mintmark soon became very well used. The “King's Norton Metal Company” became part of “Nobel Industries Ltd.” in 1918. This firm was one of those that founded “Imperial Chemical Industries Ltd.” in 1926. Around 1931 the whole minting facility was moved to Kynoch Works, Witton (in what is now Herford and Worcester). Kynoch Works was the headquarters of the what was then “ICI Metals Division”. In 1962 all of ICI’s metal interests were put under the cover of “Imperial Metal Industries Ltd.”. This name that later became just “IMI Ltd.” and the mint’s name “The IMI Mint” and then changed to “IMI plc” (no doubt following floatation of some or all of the company into public ownership). Throughout all this time the mintmark “KN” continued to be used. The most recent dated pieces I have that use this mintmark are two token types - a “1” and a “2” - for “The River Bus Partnership” dated 1990. (This page could do with an image of one of my pieces of these.). Coins were last made with the “KN” mint mark in the early 1970’s which, with the exception of the Indian example stated earlier, is when “The Birmingham Mint Ltd.” also ceased to use a mint mark on coins. Why mint marking stopped I do not know. Perhaps it was at the request of the British Royal Mint whom these mints would very often sub-contract for.