News, views & analysis blogs by: POWER PR


New Spiralock Drive Notch™ Wire Thread Inserts:

All the Benefits of Spiralock with No Tangs to Remove


Engineers seeking added joint strength in softer materials like aluminum have long used wire inserts. They´ve had a streamlined, “no tang” installation option, but they´ve never been able to combine these benefits with the vibration loosening resistance, more even load distribution, reusability, and decreased galling of Spiralock locking fasteners. Now they can with Spiralock´s new Drive Notch Wire Thread Inserts (DN™). Independent tests prove that bolts installed into the wire thread inserts have shown no loss of tension after 24 hours of continuous vibration testing (one million cycles) and no indication of fatigue problems.

Unlike tanged wire inserts, which require breaking off, retrieving and accounting for tangs, the DN™ Wire Thread Inserts require no such extra steps. Using the Drive Notch installation tool, the inserts simply thread into any NAS 1130, STI tapped hole with no need to break off, retrieve or account for tangs -- because there are no tangs. This speeds installation and improves quality, consequently reducing costs on multiple fronts. DN™ inserts eliminate the possibility of loose tangs short-circuiting electronics or causing foreign object damage. It also prevents harm to expensive castings by invasive tang removal techniques. Another benefit of DN™ is the space and weight advantage of DN™ over solid bushing type inserts, which allows the inserts to be designed into reduced diameter bosses and flanges, and into hard to reach areas.

Whether specified from the start, for repair or retrofit, the process of using a Spiralock Drive Notch Wire Thread Insert is straightforward: drill an appropriate sized hole, tap the hole with an STI tap, and install the insert. During installation, the Drive Notch installation tool locks into the insert Driving Notch to thread the insert into the tapped hole. DN™ inserts install into the same tapped hole as standard tanged inserts per NASM33537; Assembly and Dimensions, and are made from the same stainless steel material per AS7245. In addition, they meet the applicable parts of the procurement specification NASM8846, Inserts, Screw Thread, Helical Coil. In aerospace applications, the assembled SDN™ inserts accommodate standard MIL-S-7742 and UNJ controlled radius root MIL-S-8879 threaded bolts.

Unlike traditional wire inserts using a 60-degree thread design susceptible to self-loosening rotational movement, stripping and shearing, the Spiralock Drive Notch Wire Thread Inserts use Spiralock´s patented 30-degree "wedge" ramp formed into a unique 5-sided wire. When wound into a coil shape, it creates the ramp at the root of the female thread. Under clamp load, the crests of the threads on any standard male bolt are drawn tightly against the wedge ramp. This eliminates sideways motion that causes vibrational loosening and distributes the threaded joint’s load throughout all engaged threads, a claim supported by a Massachusetts Institute of Technology research study. The load percentage on the first engaged thread is significantly lower than traditional thread forms, which further reduces possible bolt failure and improves product performance. The flexible coils provide a balanced distribution of dynamic and static loads compensating for errors in the tapped threads allowing each coil to share the load evenly. Conversely, in a standard tapped thread the majority of the load is taken up by the top two threads.
The mirror smooth 8 to 16 microinch finish of the DN™ inserts provides true clamping torque and reduced thread wear on the male fastener due to the extremely low coefficient of friction.

Through its superior resistance to shock, vibration, and thermal extremes, the Drive Notch Wire Inserts offer improved joint integrity in softer materials such as aluminum, zinc, magnesium and plastic. DN™ inserts are not passivated (unless customer prefers otherwise) so the stainless steel remains active for better galvanic compatibility with aluminum and magnesium parent materials. They are also available with a variety of optional coatings and platings.

DN™ inserts eliminate stress in the parent material as there is no staking, keys or lock rings necessary to hold them in place. In addition, they resist galling, chemical and environmental corrosion. They can be particularly effective in industries such as aerospace, automotive, electronics, and medical. In aerospace, for example, the wire inserts are used in applications ranging from circuit board clamps and satellite connectors to avionics box enclosures and electronically scanned arrays.

For more info on Spiralock Corp. technology and products, visit; email; call (800) 521-2688; fax (248) 543-1403; or write to them at Madison Tech Center, PO Box 71629, Madison Heights, MI 48071

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