Elastic Stop Nut Corporation of America was a manufacturer located on Swanstrom Place. From the company's website- The ESNA® story began in 1927, when a young engineer named Carl Arthur Swanstrom came to this country from Sweden. He brought with him a license to manufacture and sell a unique new self-locking fastener. The Inventor called the new fastener an “Elastic Stop® nut” because the nut remained “stopped” anywhere along the bolt threads. A non- damaging insert, fitted into the top of the nut, gripped the bolt threads firmly, holding the nut in position without seating against the work or using secondary locking devices. The only problem with the new nut was the inability to mass produce them. The next few years were spent perfecting a automatic assembly machine to insert the locking device into the top of the nut. Swanstrom perfected the machine in the early 1930’s and only four years later the Elastic Stop® Nut Corporation of America was founded. A threaded fastener, able to positively resist the loosening effect of vibration, had long been sought by manufacturers of every type of equipment. The Elastic Stop® nut proved to be the answer—totally reliable, able to reduce maintenance costs and prevent equip- ment failure. The outstanding performance of the Elastic Stop® nut was further substantiated in 1943 when the Air Force tested and issued the first approval letter to use ESNA® fasteners on military aircraft, both fuselage and engines. During WWII billions of Elastic Stop® nuts were produced for every branch of the armed services. A staggering number of applications followed on ground support and electronic equipment. In the years that followed, the ESNA® line of standard products expanded to over 25,000 parts. New types of self-locking fasteners were introduced to the product line. . . The Eslok®, self-locking hex nuts for low cost commercial grade applications, and the Collar- lok®, a hex nut with a 360° bonded nylon collar for high speed automatic assembly tech- niques. All metal locknuts were developed for applications with high heat or weight reduction requirements. This diversified line of reliable fastener products has provided Elastic Stop® nut with a solid foundatio n for long term stability and future growth. The ESNA® product line may be found in farm, automotive, mining, aerospace, marine and electrical assemblies of all types. In 1995, Elastic Stop® nut became a part of MacLean-Fogg® and MacLean-ESNA was created and maintains a 120,000 square foot facility in Pocahontas, Arkansas. MacLean-Fogg/MacLean-ESNA represent a com- pany with capabilities unparalleled in the fastener industry. If that is not enough you can read the patent application here. https://www.google.com/patents/US2150194