Self Locking Threaded Fasteners: Celebrating Spiralock's 80 Years of Helping Engineers

Eighty years ago, engineers had no idea they'd be turning to self locking threaded fasteners for the ever lighter, stronger, higher speed, higher RPM, and higher temperature designs of today. But as Spiralock Corporation of Madison Heights, Michigan (www.spiralock.com) celebrates its 80th anniversary this year, having started in 1927 as a threading tooling company, which later developed the Spiralock thread form, its self locking threaded fasteners are increasingly a solution on some of today's most critical engineering applications.

From applications such as on the main engines of the Space Shuttle orbiter, instrumentation on the Cassini-Huygens mission to Saturn and Titan, diesel turbocharger exhaust mounts for Mack Truck, tibial component implants for as well as on undersea sonar transducers, engineers in a range of industries including aerospace/military, heavy truck, medical, automotive, agriculture, construction, are finding the company's self locking fasteners superior to traditional thread locking devices.

Wherever shock, vibration, thermal stress, repeated use, assured quality, and lower maintenance/service costs are a concern, Spiralock thread locking technology is becoming a preferred engineering choice over traditional thread locking fasteners, which at best simply prevent the threads from catastrophically coming apart. Because none actually holds the clamp load in the joint, they are susceptible to vibration, fatigue, or temperature-related joint failure.

The basic design problem stems from the standard 60-degree thread form: the gap between the crest of the male and female threads can lead to vibration-induced thread loosening. Stress concentration and fatigue at the first few engaged threads is also a problem, along with an increased probability of shear, especially in soft metals, due to its tendency toward axial loading. Temperature extremes can also expand or contract surfaces and materials, potentially compromising joint integrity.

To address these reliability concerns while reducing component weight and enabling re-usability, engineers have turned to the first thread innovation since WWII, Spiralock self locking threaded fasteners. This re-engineered thread form adds a unique 30-degree wedge ramp at the root of the thread which mates with standard 60-degree male thread fasteners.

The wedge ramp allows the bolt to spin freely relative to female threads until clamp load is applied. The crests of the standard male thread form are then drawn tightly against the wedge ramp, eliminating radial clearances and creating a continuous spiral line contact along the entire length of the thread engagement. This continuous line contact spreads the clamp force more evenly over all engaged threads, improving resistance to vibrational loosening, axial-torsional loading, joint fatigue, and temperature extremes.

The innovative locking fastener compensates for variations in manufacturing tolerance and process due to mass production with its locking thread actually inside the joint. This eliminates the need for secondary locking devices or procedures, and can significantly reduce costly warranty claims and potential liability.

As Spiralock celebrates its 80th corporate anniversary, its self locking fasteners have been used in the manufacture of thousands of applications across North America, South America, Asia, and Europe. Production changeovers to these self locking fasteners often require just an exchange of traditional nuts, wire inserts or simply drilling out and re-tapping existing parts stock that have unreliable standard tapped holes.


For detailed test data, including comparative graphic loading characteristics or photoelastic analysis/load vector comparison animation, visit Spiralock at www.spiralock.com; call (800) 521-2688; fax (248) 543-1403; or write to Spiralock at Madison Tech Center, PO Box 71629, Madison Heights, MI 48071.

Spiralock Corporation
Kate Turowska
Phone: (248) 543-7800
Fax: (248) 543-1403
http://www.spiralock.com