Wikipedia
Struthers-Dunn LLC, formally known as Struthers-Dunn or Dunco, is a manufacturer of industrial controls since 1923.
Struthers-Dunn was founded by John Struthers-Dunn in 1923 outside Philadelphia, Pennsylvania. They were one of the earliest relay manufacturers in the United States and became the first manufacturer of Military Relays for US Government during World War II. Their first military product, the 101 Series contactor was a 100A rated SPST switch for use on Naval Ships in 1938. Subsequent development led to the beginning of the QPL (Qualified Product List) of products for the US Military, commonly known as MIL-SPEC Products today.
On the Commercial Products side, their other notable design was the 219 Series of Industrial Relays. Originally designed as a socket-compatible, high-reliability relay for use in Nuclear Energy Facilities, it is still used today for critical controls. The 219 packaged family of products, and the 219NE (Nuclear Energy) family, encompassed in addition to the standard electro-mechanical versions - the 236/237/238 family of industrial time-delay relays, the later 246/247/248 family of advanced time-delay relays, the 255 Series of latching relays, the 311 Series of Sequence/ stepper relays, the 349 Series Voltage Sensors and the RSX Series of custom packages controls.