Self-Locking Key Inserts

Stanley Engineered Fastening now incorporates its self-locking Spiralock internal thread form design, which reportedly has superior resistance against self-loosening when exposed to harsh environments involving significant shock, extreme vibration, and drastic thermal cycling, into key locking threaded inserts.

When designing components and threaded assemblies, the solid body key inserts are often considered as the most durable and robust threaded insert option; the key inserts provide the strongest thread reliability and load carrying capacity in many materials.

When compared to a tapped hole or other threaded inserts, the key inserts will have the highest pull out strengths in all materials due to the staking of the keys and tubular insert body design. Spiralock key inserts can be used in virtually any material, such as plastic, aluminum, cast iron or steel parent materials. Furthermore, Spiralock threads and fasteners allow for nearly unlimited reusability since the wedge locking feature does not degrade or diminish with repeated installs and exposure to harsh situations.

For aerospace, the MS51830-2/NAS1395 Spiralock commercially equivalent key inserts provide the strongest thread option in softer materials such as aluminum as well as other materials. The key inserts are available with the Spiralock internal thread form as small as a 2-56 or M2 and as large as a 1-12 or M24. The Spiralock key inserts are available as a miniature, lightweight, heavy duty and extra heavy duty wall body, each type having varying wall thicknesses depending on customers' requirements.

Additionally, when other threaded inserts are not possible, the key inserts can often serve as a "last option" thread repair for expensive components since the solid body key insert threads are significantly more robust than wire inserts, molded inserts, or ultrasonic inserts.

Any industry requiring damaged thread repair, such as oil and gas, automotive, trucking, construction, or aerospace, will find Spiralock key insert provide a thread that can prevent the scrapping of an expensive part. The keys, which stake into the parent material like anchors, create a positive mechanical lock against rotation, eliminating the insert's rotational movement within the parent material. This feature prevents the insert from pulling out of the material and allow for use of higher torques when compared to other types of threaded inserts.

Spiralock threads and fasteners have been proven in thousands of applications over many years. The Spiralock threads and fasteners accept standard male fasteners, eliminate the need for other locking devices, provide for extensive reusability, minimize the risk for galling since it is free spinning, and substantially reduce the potential for fatigue failure compared to standard threads.

The Spiralock thread form solves thread loosening and joint integrity issues by changing the physics of how the threads interact. In traditional 60 degree threads, the gap between the crests of the screw/bolt and the major diameter of the internal thread is the area where loosening originates.

With significant transverse motion, thermal variances or impact and shock, microscopic movements and preload reductions occur and this very small clearance gap allows the bolt to minimally "slip" relative to the major diameter of the female threaded hole. Once preload begins to diminish at a consistent basis while in service, the joint is considered a failure and will lose the majority of clamp load during service. Furthermore, with standard threads, most of the loads are carried by the first couple threads. Stress concentration and fatigue at the first few engaged threads can lead to premature joint failures.

When using the Spiralock self-locking thread profile, it has been observed and proven that the wedge lock profile eliminates the clearance gap, locking the male fastener in place. Spiralock is free running and begins to lock once torque is applied, and tension is created between the male fastener and the Spiralock threads. This allows for a quick and smooth bolt rundown without significant resistance or drag when threading components.

The Spiralock wedge ramp creates line contact with the screw/bolt along the entire length of thread engagement, preventing any movement between the screw/bolt and Spiralock wedge locking ramp. Therefore, the Spiralock threads provide optimal results, quick fastener assembly, offering the best opportunity to resist self-loosening in any harsh environment while permitting extensive thread locking reusability for product longevity.

Since the key inserts are manufactured with solid bodies, they are virtually impossible to cross thread during installation, which streamlines assembly and quality control. The key inserts install into standard threaded hole, using a standard drill and tap to the required external thread size for each type and size key insert. The composition of the key inserts, available in AISI 4140 steel, grade 303 stainless steel, and A286 stainless steel, provide heat and corrosion resistance, with A286 providing additional strength. Options for coatings include dry film lube or cadmium plating which provide additional lubricity and further galvanic corrosion protection for the internal threads.