Great Britain 1973 3p ultramarine, SGX855bGreat Britain 1973 3p ultramarine (2 bands), SGX855b. Very fine unmounted mint, with full original gum, top left hand corner marginal imperforate pair. A very scarce imperforate Machin pair, particularly in positional form and in such pristine condition. GB Specialised Catalogue No: U104a. The Machin series of postage stamps is the main definitive stamp series of Great Britain, since 5 June 1967. The design by Arnold Machin consists simply of the