Circular date handstamp
Bruno, Nebraska, postal workers marked the back of mail pieces "received" with this handstamp. The practice of backstamping mail, that is marking mail when it was received at a post office, was discontinued in mid-1913 by order of Postmaster General Burleson.
The mortise is tall enough to accomodate four pieces of steel type, stacked upon each other and secured by the set screw. These represented the month, date, time, and year. The set screw visible in the photo was thumb-tightened; later versions had a square head and used a socket-key to tighten or loosen the screw.