A bolted joint holds because of clamp load, not because the threads feel tight. Once the mating parts start sliding sideways against each other, that clamp load bleeds off and the fastener backs itself out. NASA’s Fastener Design Manual (RP-1228) puts hard ceilings on the two fixes most teams reach for first. The best anaerobic thread-locking adhesives function at 450 degrees F and the worst quit at 200 degrees F. Nylon locking collars and pellets stop at roughly 250 degrees F.
The same manual is blunt about the cheapest option on the shelf. A helical spring lock washer sits flat by the time the bolt is fully torqued, and NASA calls a lock washer of that type “useless for locking.”
Three of the four locking methods on a typical print carry a limit that turns into a warranty claim later. Here is how each anti-vibration option behaves under transverse load, heat, and repeat service.
| Locking Method | Transverse Vibration Resistance | Temperature Limit | Reuse | Removal |
|---|---|---|---|---|
| Anti-Vibration Wedge-Lock Washers (Component Solutions Group) | Highest; adds tension when rotation starts | Set by the base alloy | Fully reusable | Standard hand tools |
| Anaerobic Threadlocker | High once cured; fills thread clearance | 200 to 450 degrees F by grade | Single use; threads need cleaning | Heat plus high breakaway torque |
| Nylon-Insert Locknut (Prevailing Torque) | Moderate | About 250 degrees F | Grip drops after first removal | Standard hand tools |
| Deformed-Thread All-Metal Locknut | Moderate to high | Limited only by parent metal and plating | About 10 reuses | Standard hand tools |
| Helical Spring (Split) Lock Washer | None once flattened | Set by the steel | Reusable but non-functional | Standard hand tools |
Why Bolted Joints Come Loose in Service
Premature structural failures usually trace back to a fastener that stopped holding, not one that broke. Standard nuts and bolts depend on friction created by the tightening torque. Cyclic side loads defeat that friction. Engineering and procurement teams hit the same nine problems when commodity hardware goes into a high-vibration assembly.
- Transverse slip: side-to-side movement between the joint faces overcomes thread friction and lets the nut rotate. NASA describes this lateral movement as the motion that causes loosening under vibration.
- Thermal cycling: joined materials expand and contract at different rates. Every cycle sheds a little tension, and the joint gets easier to shake loose.
- Embedment and coating relaxation: paint, plating, and gaskets settle under load in the first hours of operation. Short-grip joints lose the largest share of preload this way.
- Buried joints: fasteners inside a gearbox or behind a weldment never get retorqued. They need a locking element that survives the full service life without inspection.
- Thread fretting: micro movement wears the flanks long before the bolt reaches its fatigue limit. The joint degrades quietly, then fails all at once.
- Mating surface hardness: any locking element that bites the surface needs a surface softer than its teeth. Hardened, ground, or heavily coated faces defeat that grip.
- Robotic and automated assembly: anaerobic threadlocker needs dispensing control and cure time. A robotic cell running to takt time either slows down for that step or skips it, and both outcomes cost more than the adhesive.
- Galling on stainless installs: high-speed pneumatic drivers generate enough friction heat to cold-weld A2 and A4 stainless threads. The nut seizes short of preload, so the joint reads tight while carrying almost no clamp load.
- Part-number sprawl: adhesive from one vendor, prevailing-torque locknuts from a second, washers from a third. Each locking system on a high-vibration C-parts program carries its own lead time, minimum buy, and stock-out risk.
What the Junker Transverse Vibration Test Proves
DIN 65151, the Junker test, is the reference method for locking performance. The rig clamps a bolted joint, drives it with forced transverse shear motion, and records remaining clamp load through a load cell for the full run. The output is a curve, not an opinion.
Plain nuts and bolts fail that curve almost immediately. Once the lateral shear starts, an unsecured nut walks loose in seconds. Axial pull tests never show this, which is why joints that pass a tension check still come apart in the field.
Surface friction buys some resistance. NASA cites SPS Technologies data showing serrated-face Durlock 180 bolts require 110 percent of the tightening torque to loosen them, with excellent vibration resistance in company testing. That holding power costs you gouged bearing surfaces. Before comparing locking elements, confirm the joint actually reaches target preload using our torque and preload calculator. No locking element rescues a joint that was undertightened on the line.
Vibration-Resistant Anaerobic Threadlockers: Strong Hold, Single Use
Anaerobic adhesives cure in the absence of air and fill the clearance between mating threads with hard polymer. The cured film blocks the micro movement that starts self-loosening, and it seals the threads against moisture and fluid leakage.
Grade matters more than brand. Removable grades come apart with hand tools. High-strength grades need heat plus serious breakaway torque. Temperature decides the rest: NASA puts the best adhesives at 450 degrees F and the worst at only 200 degrees F, so a hot gearbox or an engine bay eliminates most of the shelf.
- Fills thread clearance completely and seals the joint against corrosion.
- Works with standard bolts and nuts, so the drawing does not change.
- Cure time slows the line and adds a process step operators skip under pressure.
- Threads need wire-brushing and fresh product before reassembly, which rules it out for parts that come apart on a maintenance interval.
Best fit is a permanent joint that stays below the grade rating and rarely gets serviced.
Nylon-Insert Locknuts: Cheap, Fast, Temperature Limited
A nylon-insert locknut, commonly called a Nylock nut, carries an unthreaded nylon collar at the top of the nut. The bolt threads bind against that collar, and the interference fit resists rotation even after clamp load drops. That is why it remains the default prevailing-torque part in general manufacturing.
Heat and reuse are the limits. NASA sets the maximum operating temperature of the nylon pellet and locking collar at about 250 degrees F, and states the nylon is damaged quickly by reassembly. Stainless assemblies add a second problem, since galling between stainless threads seizes a nut before it reaches preload.
- Inexpensive, stocked worldwide, and installed with standard tooling.
- Locks immediately with no cure time and no added process control.
- Loses grip after the first removal, so joints on a service schedule need a new nut every time.
- The collar seals against gas and moisture leakage, a useful side benefit at low temperature.
Where heat rules out nylon, the all-metal deformed-thread locknut is the direct swap. Its temperature range is limited only by the parent metal and its plating, and NASA puts its life at roughly 10 reuses before the locking feature is spent. Specify the nylon version for low-heat, single-install joints on light industrial equipment.
Anti-Vibration Wedge-Lock Washers: Tension Instead of Friction
Wedge-locking washers work in bonded pairs. The outer faces carry radial teeth that grip the bolt head and the joint surface. The inner faces carry cams, and the cam angle is greater than the thread pitch angle of the bolt.
Rotation is the trigger. If vibration turns the bolt even slightly, the cams ride up on each other and lift the head, which raises tension in the joint instead of releasing it. NASA describes the same wedge principle in the Spiralock thread form, where a 30 degree ramp at the thread root makes the lateral movement that causes loosening nearly impossible.
Two conditions break the mechanism. Mating surfaces harder than the washer teeth stop the outer faces from gripping, and soft base material lets the teeth embed and settle. Match washer hardness to the joint, and confirm the bolt is hardened enough to carry the added tension.
- Highest transverse resistance of the four methods, and the only one that gains tension when loosening starts.
- Temperature is set by the alloy, not by a polymer or an adhesive.
- Reusable, and removed with ordinary hand tools instead of a heat gun.
- Installs in one motion with no cure step, which suits automated and robotic assembly cells.
- Higher piece price than a nylon insert or a drop of adhesive, which is the real barrier on cost-driven programs.
CSG stocks wedge-locking lines including DISC-Lock and Superloc, alongside the engineered brands we distribute for OEM programs. Specify these on heavy equipment, rail, mining, and any safety-critical joint that sees constant shock.
Split and Tooth Lock Washers: Take Them Off the Print
Helical spring washers and tooth washers rely on biting the surface. Under full torque the split washer flattens into what amounts to a solid flat washer, and NASA states plainly that a lock washer of this type is useless for locking. Tooth washers do bite, but they damage the mating surfaces, and NASA warns those scratches cause crack formation in highly stressed fasteners and mating parts, plus higher corrosion susceptibility.
Both parts still ship by the barrel because they cost almost nothing. On a vibrating assembly they buy nothing except a visual cue that somebody tightened the bolt.
- Negligible piece cost and available in every size and grade.
- No measurable transverse vibration resistance once flattened.
- Surface gouging raises corrosion and crack risk on critical parts.
Leave them on static joints with zero transverse movement, and nowhere else.
Matching the Right Locking Method to Your OEM Build
Six inputs settle the decision: peak operating temperature, service interval, joint access, mating surface hardness, how the joint gets installed on the line, and the cost of a single field failure. Anything above 250 degrees F removes nylon inserts. Anything above the adhesive grade rating removes chemical lockers. Joints torn down on a maintenance schedule need a reusable mechanical element. Buried joints nobody will ever retorque need the method with the best transverse test data, whatever the piece price. For the full range of options, including chemical and mechanical methods, see our overview of thread locking methods.
Installation method breaks the remaining ties. Automated cells favor a mechanical element that seats in one motion, because a cure step is the first thing dropped when the line runs behind. EV battery enclosure fasteners sit at the hard end of the list, since the pack carries road vibration for the life of the vehicle behind limited service access.
Run the math on total cost, not unit cost. A wedge-lock washer that costs cents more than a nylon nut is cheap against one warranty teardown on a machine in the field. Routing the whole locking program through one global sourcing partner also removes the part-number sprawl that comes from splitting adhesives, nuts, and washers across three vendors. Our Design Assist engineering team reviews the joint, the material stack, and the assembly process before anyone changes a part number.
Component Solutions Group is a Bufab company headquartered in Dayton, Ohio, supplying engineered C-class components to OEM and Tier 1 manufacturers. We source through the Bufab network of 1,600+ suppliers across 30+ countries, hold ISO 9001:2015 and AS9120 Rev B, run IATF 16949 certified automotive supply through A1 Fastener & Components, and ship at a 99.9% order accuracy rate. ITAR compliance, material test reports, and full traceability come with the documentation package.
Specify the locking method before the first production run, not after the first field return. Submit an RFQ with your joint details, or request a sample kit and run it on your own transverse vibration fixture. For more, see our guide to bolt failure analysis.
Frequently Asked Questions (FAQs)
Can Nylock nuts be reused?
Not in a critical joint. The NASA Fastener Design Manual states the nylon locking element is damaged quickly by reassembly, so grip falls off after the first removal. Use a fresh nut, or move to an all-metal deformed-thread locknut rated for roughly 10 reuses.
How hot can thread locking adhesive get?
NASA puts the best anaerobic thread-locking adhesives at 450 degrees F and the worst at only 200 degrees F, so check the specific grade before you spec it. Above that band, use an all-metal mechanical locking method.
What is the standard test for fastener vibration resistance?
DIN 65151, the Junker test. It drives a bolted joint with forced transverse shear motion and records remaining clamp load throughout the run. Axial tension tests miss the self-loosening mechanism entirely.
Does a split lock washer stop vibration loosening?
No. Once the bolt is fully torqued the washer is flat and behaves like a plain flat washer. The NASA Fastener Design Manual calls a lock washer of this type useless for locking.
