Wire thread inserts eliminate need to account for tangs

February 12, 2008

Spiralock says that, in independent tests, bolts installed into the company's Drive Notch (DN™) wire thread inserts showed no loss of tension after 24 hours of continuous vibration (1 million cycles) and no indication of fatigue problems.

With the installation tool, the inserts thread into any NAS 1130, STI tapped hole. The inserts eliminate the need to account for tangs, the company reports. In addition, the inserts can be designed into reduced-diameter bosses and flanges and into hard-to-reach areas. The user drills and taps a hole with an STI tap, and then installs the insert. The installation tool locks into the insert, threading the insert into the tapped hole.

According to the company, the inserts install into the same tapped hole as standard tanged inserts per NASM33537; incorporate the same assembly and dimensions; and are made from the same stainless steel material per AS7245. They meet the applicable parts of the procurement specification NASM8846. In aerospace applications, the assembled SDN™ inserts accommodate standard MIL-S-7742 and UNJ controlled radius root MIL-S-8879 threaded bolts.

Suitable for softer materials such as aluminum, zinc, magnesium, and plastic, the inserts use the company's patented 30-degree wedge ramp formed into a five-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. The flexible coils provide a balanced distribution of dynamic and static loads to compensate for errors in the tapped threads and allow each coil to share the load evenly.

No staking, keys, or lock rings are necessary to hold the inserts in place. They are designed to resist galling, as well as chemical and environmental corrosion.

Applications include aerospace, automotive, electronics, and medical. Various optional coatings and platings are available.