Validator for money orders
Validator machines were introduced in the 1870s. B. B. Hill received a patent for this machine's characteristics in 1876. The validator consists of two principal components: 1) the body used by the postal employee to emboss a money order validation imprint upon documents; and 2) a brass die seated over brass month, date, and year wheels. The brass die has the city and state of the post office plus the letters "M O B" (Money Order Business). An opening in the center of the brass die allows a selected month, date, and year to be imprinted. The item to be validated was laid face-up upon the small, circular, rubber cushion under the imprinting area. When the top striker cap was hit with a fist, an imprint was made by the plunging die and date wheels behind an inked ribbon.
This style of validator, as well as other variations, was also used by railroad, airline, motor-coach, and steamship lines for validating tickets and receipts. Post Office Department usage is distinguished by the die bearing the "M O B" characters at the bottom of the dial. The majority of money orders and receipts were validated by rubber dating stamps that likewise bore "M O B" in the die's lettering.