The standard weight of these pieces was 24 to the pound avoirdupois (2/3 ounce or 291.7 grains each). This design was also produced as proof strikes with various base and precious metal planchets. The Fourth Issue of George III pennies (dated 1806-1808) features numerous patterns and proofs alongside regular copper currency pieces. Proof pennies, halfpennies and farthings were given to visiting dignitaries at Soho. It was a good way to publicise the fine workmanship of Boulton and Watt's fledgling mint and to cement it's place at the heart of the industrial revolution. The dies were heavily used and were thus reworked with the pennies being restruck for some years with no alteration to the date. Copper, bronzed and gilt proofs exist as well as some extremely rare proofs in silver, gold and platinum. For further details of the issue please refer to C.W. Peck's monumental work, "English Copper, Tin and Bronze Coins in the British Museum 1558 - 1958," second edition, 1970, page 364.