sentences:  The diameter was made strictly defined by striking within a collar so that diameter, thickness and weight could be used to prove the quality of the metal.In 1797 the first, and only, copper twopence and the first penny coins were produced under contract although the smaller denominations did not follow until later.These coins were comparatively large, having a broad raised rim with the inscription pressed below the surface and became known as the "cartwheel" pennies.