 Decimal rates had previously appeared on some coils of the 1975 Americana Series.Because of their heavy use by businesses mailing to households, vast quantities of these were produced, and were a common sight in the daily mail of the 1980s and 1990s.Plate numbers were printed in small letters at the bottom of the stamps at intervals of twenty-four, forty-eight, or fifty-two depending on the printing press employed and these stamps are known as plate number coils.