Struthers-Dunn Inc, 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.