The unique, all-metal Dyna-Thred II design is a technological breakthrough in reliable self-locking fasteners. Extensive tests prove that the locking action of Dyna-Thred II fasteners maintains minimum torque requirements after more than 15 re-uses.

The patented Dyna-Thred lock is formed of the fastener itself and requires use of no additional locking element materials. Locking action takes place in a full hoop, 360° around the thread, providing an equal load on all sides. Dyna-Thred II fasteners are available in a wide variety of head styles, materials, finishes, and sizes.

The useful temperature range of Dyna-Thred II fasteners is limited only by the physical characteristics of the parent bolt material. From cryogenic applications to sustained high temperatures, Dyna-Thred II fasteners stay locked in.

Typical Applications

Use Dyna-Thred II fasteners whenever extreme heat and punishing vibration loosen or destroy other fasteners.

• Airborne turbo-prop engines
• Ground-based turbines
• Commercial and military aircraft braking systems
• Auxiliary power units
• Rapid transit and rail subsystems

The Dyna-Thred II Principle

The Dyna-Thred II lock is made by forming a close tolerance hole axially into the threaded end of a fastener. A controlled area of the cavity is dilated to expand the periphery of a controlled threaded area. The pitch diameter of the first thread is left unchanged for starting ease.

The result: an easily installed, highly reliable, self-locking bolt or screw. Dyna-Thred II bolts meet all the performance requirements of, and is qualified to, Specification MIL-F-8961.



Dyna-Thred II Materials and Finishes

The following are the results of laboratory tests independently conducted by Almay Research & Testing Corporation, Los Angeles, California. Complete certified results are available on all tests. For more result details, Download this page (76Kb Adobe Acrobat PDF file).

Static Tensile Strength Tests
Dyna-Thred engagement was affected 2 threads above the cavity area. Comparisons were made between standard NAS1004 and Dyna-Thred at room temperature and Dyna-Thred alone at 1200°F. Tests proved that essentially no tensile strength difference existed between NAS1004 bolts and Dyna-Thred bolts.

Tension-Fatigue Tests
Dyna-Thred was tested with the essentially comparable NAS1004 bolt to determine their strength characteristics. No appreciable strength difference between the two types of bolts was noted.

Stress Rupture Tests
Dyna-Thred bolts were positioned so that 1-1/2 threads protruded through the end of the nut. The bearing face of the nut was within approximately 3 threads of the runout. The Dyna-Thred bolt and nut assembly was heated to 1200°F during the test period of 23 hours. All test bolts satisfactorily met stress rupture test requirements of Specification AMS 7478. † All Dyna-Thred bolts were corrosion-resistant steel fabricated from A286 and silver plated. Unplated hexagon A286 nuts were used in accordance with dimensions specified in MIL-DTL-18240D.

15-Cycle Locking Torque Tests (Meets MIL-F-8961 Torque Requirements)
Tests described were run at room temperature and after 1200°F bake for six hours, in accordance with military specification MIL-F-8961. All bolts tested were manufactured from A-286 CRES, and were Dyna-Thred part number DTF1004-21A, which has a ¼-28 UNF-3A thread. Results indicated are minimum breakaway values measured in inch-pounds.



How to Specify

Please download this page (76Kb Adobe Acrobat PDF file) for detailed specifying information.



Applicable Standards

Military Specifications
MIL-F-8961

Commercial Standards
IFI 124, IFI 524 (Metric)



Additional Materials and Finishes

Additional Materials and Finishes are available upon request. Not all Material/Finish combinations are available for every head style.

Thread Fit Classes and Configuration Envelope

Unless otherwise specified, thread fit classes and configuration envelope dimensions are per the applicable head style ANSI/ASME commercial standard.

Tensile Strength

Studies have shown that the greatest percentage of tensile load of a fastener is carried in the first two threads of engagement in the mating thread form. As evidenced by the static tensile test described on Page 25, DynaThred fasteners easily meet minimum tensile strength requirements when used in this way.

Minimum Mating Thread Engagement

The standard drilled cavity depth of a typical Dyna-Thred fastener is approximately 7 thread pitches. For this reason, mating thread engagement of 9 threads minimum is required to ensure tensile strength performance consistent with test results on Page 25. Prevailing torque performance, however, can be achieved with thread engagement of 7 threads, minimum.



See for Yourself

Send us a sample of your part or fastener, along with a brief description of its application and performance requirements, and we’ll process it using the most appropriate Long-Lok thread locking or sealing method. Or, to sample a standard Long-Lok fastener, simply supply us with a part number. Samples are provided free of charge. Call your nearest Long-Lok facility for assistance.