In space, joint loosening or joint failure is not an option. That is why NASA engineers choose Spiralock key inserts to fasten various parts of the main engines of the Space Shuttle, the Saturn Cassini orbiter and Titan Huygens probe. The self-locking internal thread form design resists self-loosening when exposed to harsh environments involving significant shock, extreme vibration, and drastic thermal cycling.
The solid body key inserts are a durable and robust threaded insert option. The key inserts provide strong thread reliability and load carrying capacity in many materials.
When compared to a tapped hole or other threaded inserts, the key inserts will have high pull out strengths in all materials due to the staking of the keys and tubular insert body design. These key inserts can be used in almost any material, including plastic, aluminum, cast iron, or steel parent materials. Furthermore, the threads and fasteners are reusable since the wedge locking feature does not degrade or diminish with repeated installs and exposure to harsh situations.
For aerospace, the MS51830-2/NAS1395 commercially equivalent key inserts provide a strong thread option in softer materials such as aluminum. The key inserts are available with the internal thread form as small as a 2-56 or M2 and as large as a 1-12 or M24. They are available with miniature, lightweight, heavy duty and extra heavy duty wall body, each type having varying wall thicknesses depending on requirements.
Additionally, when other threaded inserts are not suitable, the key inserts can serve as a “last option” thread repair for expensive components since the solid body key insert threads are 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 these key inserts provide a thread that can prevent scrapping 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 allows the use of higher torques when compared to other types of threaded inserts.
The Spiralock threads and fasteners accept standard male fasteners, eliminate the need for other locking devices, are reusable, minimize the risk for galling, and substantially reduce the potential for fatigue failure.
The thread form solves thread loosening and joint integrity issues by changing the physics of how the threads interact. In traditional 60° 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 load is carried by the first threads of the inserts. Stress concentration and fatigue at the first few engaged threads can lead to premature joint failures.
With this self-locking thread profile, the wedge lock profile eliminates the clearance gap, locking the male fastener in place. The inserts are free running and begin 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 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 for the most 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 holes, 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.