Wedge Lock Washers vs Nylon Insert Nuts, Split Washers and Jam Nuts

Quick answer: Nylon insert nuts, split washers, jam nuts and prevailing torque nuts all rely on friction to resist loosening. Friction varies from joint to joint and drops away under vibration and dynamic loading. A wedge lock washer works differently. It uses a pair of interlocking cam faces with an angle steeper than the thread pitch, so any rotation has to lift the bolt against the cams. That increases clamp load instead of releasing it. In Junker testing to ISO 16130 and DIN 25201, clamp load is measured across 2,000 cycles and a pass requires retaining 80% or more of the original clamping force. LNA’s WW Series Wedge Washer holds above that threshold. The friction-based methods tested alongside it do not.

If you have ever re-torqued the same bolt on the same machine twice in a year, this comparison is the reason. The question is not which locking device is strongest. It is which one relies on friction and which one relies on geometry, because those two things behave completely differently once a joint starts moving.

Why do friction-based locking methods lose clamp load?

Every common locking method except a wedge lock washer works by adding friction somewhere in the assembly. The friction either sits under the bolt head or nut, or it sits on the thread itself.

That works until the joint moves. Vibration and dynamic loading produce tiny relative movements between the bolt, the nut and the clamped parts. Each movement lets the fastener rotate a fraction. Once rotation starts, the friction that was holding it has less clamp load to work with, so the next movement rotates it further. The loss compounds.

Single lock washers rely on friction and serrations. That friction varies between joints, even on the same application, so it cannot guarantee a locked connection. Prevailing torque nuts grip the thread and keep the nut from backing off the bolt, but they do not keep it from loosening under vibration or dynamic loads, and clamp load drops off from as little as a quarter turn.

A quarter turn is the detail that matters. That is not a failure anyone catches on a routine inspection. The nut is still there. It is still tight to the touch. The preload that was doing the structural work is mostly gone.

Nylon insert nuts

A nylon collar in the top of the nut deforms around the thread and creates drag. It keeps a nut from backing off completely, and it is inexpensive and widely stocked. The nylon has a limited temperature range, loses effectiveness on reinstallation, and adds thread drag rather than a physical lock, so it does not hold preload under sustained dynamic loading.

Split lock washers

A split spring washer flattens under tightening and pushes back against the nut, with the split ends digging in slightly. The load it can store is very small compared with the preload in a properly tightened structural bolt, and once the joint is fully torqued the washer is essentially flat, contributing friction rather than spring force.

Jam nuts

Two nuts are tightened against each other so the thread flanks load in opposite directions. Done correctly it is genuinely effective and needs no special parts. It also doubles the installation steps, requires the thinner nut in the correct position and the correct tightening sequence, adds stack height, and still depends entirely on thread friction. In the field it is very often installed backward.

All-metal and prevailing torque nuts

A deformed or slotted metal section grips the thread. This handles heat far better than a nylon insert and can be reused more readily. The mechanism is still thread friction, which is why it shows the same quarter-turn sensitivity as the other friction methods under test.

How does a wedge lock washer actually work?

A Wedge Washer is supplied as a pre-glued pair and installs as though it were a single washer. The adhesive is there to keep the two halves correctly oriented during installation and has no technical function once the joint is fitted.

Each half has two working faces:

• The outer face is hardened and serrated. It bites into the bolt head, the nut and the mating surface. The serrated faces are designed to be harder than most commonly used fasteners so they can key into the joint components.
• The inner faces carry angled cams that interlock, and the cam angle is steeper than the thread pitch of the bolt.

That cam angle is the whole mechanism. Because the serrations have keyed the outer faces to the bolt head and the mating surface, any loosening rotation has to happen between the two cam faces. And because the cams are steeper than the thread, rotating the bolt one increment lifts it further up the cam ramp than the thread lets it travel down. The bolt has to stretch. Stretching a bolt is exactly what preload is, so the attempt to loosen the joint increases clamp load rather than reducing it. This is the wedge effect.

The joint can still be disassembled, but only by deliberate loosening, which forces the cam faces up and over each other. No re-tightening is required once the joint is in service.

What does the Junker test show?

The Junker test is the industry method for assessing fastener self-loosening. It drives transverse movement between the bolt, nut and clamped joint under dynamic load, which is the condition that defeats friction, and it measures clamp load continuously while it does so.

LNA tests the WW Series to ISO 16130 and DIN 25201. Clamp load is measured across 2,000 cycles, and a pass requires maintaining 80% or more of the original clamping force.

Compared with traditional locking methods, the Wedge Washer is the only product consistently to meet that benchmark. Five friction-based assemblies are tested alongside it:

• Nylon insert nut
• Mechanical lock nut
• Split lock washer
• Hex nut with flat washer
• Hex nut with no washer

There is also a simple visual record. Before testing, a line is marked across the bolt head, both washer halves and the mating surface. After 2,000 cycles the Wedge Washer marks are still aligned, showing the joint stayed locked. On the split lock washer the marks have separated. On the prevailing torque nut, roughly a quarter turn of movement is enough to lose most of the clamp load.

If you want the background on why joints loosen in the first place, our guide to bolt loosening due to vibration covers the underlying mechanics.

Which locking method should you specify?

Suitability recommendations reflect LNA engineering guidance. Locking mechanism and clamp load performance reflect tested catalog data.

Where do wedge lock washers get used?

The WW Series is specified in machine building, oil and gas, manufacturing and processing, recycling, medical equipment, and power generation including wind turbines.

The pattern across all of those is the same. The joint moves, and getting a technician back to the bolt is either expensive, dangerous or both. A shredder rotor, an offshore skid, a turbine nacelle and a high-speed production line have nothing in common except that nobody wants to re-torque them on a schedule.

For LNA customers the natural pairing is with steel connection hardware. A BeamClamp or BoxBolt connection in a vibration-exposed structure is exactly the case where the connection itself is sound and the preload is the variable worth protecting.

How many wedge lock washers does a joint need?

A Wedge Washer belongs on any side of a bolted joint where rotation could let the joint loosen.

• Blind connection, where the fastener can only loosen in one direction: one Wedge Washer.
• Through-bolted joint, where loosening could occur from either side: two Wedge Washers, one under the bolt head and one under the nut.

What materials and sizes are available?

The WW Series comes in five materials, each in Standard and Large Diameter (LD) versions.

Selection is three decisions: bolt diameter, then Standard or Large Diameter, then material and finish. The mild steel range spans washer codes WW-M3 through WW-M130, covering US bolt sizes from #5 up to 5 inches.

Why does lubrication matter more than the locking device?

This is the part most specifications skip. There is no single torque value suitable for every application. Material strength, friction, clamping length and embedment all change the result, and because friction dominates torque accuracy, LNA recommends lubrication wherever possible.

That effect is bigger than most people expect. For a Grade 5 zinc plated M16 fastener, the catalog guideline gives 151.21 ft-lbs with oil producing 16,861 lbf of clamping force, against 153.4 ft-lbs dry producing 13,938 lbf. Effectively the same torque wrench setting, roughly 17% less clamp load.

On stainless assemblies LNA always recommends a lubricant, both for clamp load consistency and to avoid thread galling.

Full tightening torque and clamp load tables for every material are in the Wedge Washer catalog. Those figures are guidelines. Each critical bolted joint should be analyzed individually by a design engineer.

Frequently Asked Questions

Can wedge lock washers be reused?

They can be removed and reinstalled. The pair is supplied pre-glued for correct first installation, and once installed the adhesive has no technical function. If the joint is disassembled, the washers separate into two pieces and must be reinstalled correctly, cam faces together and serrated faces outward.

How do I confirm a wedge lock washer is working?

There is a physical check. Tighten the joint to the specified torque, mark a vertical line across the bolt head or nut, both washer halves and the mating surface, then loosen the joint. If it is functioning correctly, the line on the mating surface stays aligned with the washer half touching it, while the line on the bolt head or nut separates. That confirms serration engagement and cam action.

Will a wedge lock washer work on soft materials?

Not necessarily. The washer has to bite into the bolt head or nut and into the mating surface. The hardened serrated faces are designed to be harder than most commonly used fasteners, but if a surface is too soft, such as certain plastics or polymers, correct function may not be achieved and suitability should be verified first. Compare the washer hardness values against the materials being joined.

Is a wedge lock washer better than a nylon insert nut?

For joints under vibration or dynamic loading, yes, and the difference is mechanism rather than degree. A nylon insert nut adds thread friction. A wedge lock washer adds a physical cam lock. In Junker testing to ISO 16130 and DIN 25201 across 2,000 cycles, the nylon insert nut is one of the friction-based assemblies that does not hold the 80% clamp load threshold. For a low-vibration assembly at ambient temperature, a nylon insert nut is often perfectly adequate and cheaper.

Do wedge lock washers need re-tightening?

No. Because the cam geometry resists loosening rather than relying on friction that decays, no re-tightening is required, which reduces maintenance and gives long-term confidence in the joint.

What is the difference between Standard and Large Diameter wedge washers?

Large Diameter (LD) versions have a larger outside diameter for the same bolt size, which spreads the bearing load over more of the mating surface. Selecting between them is the second of the three selection steps, after bolt diameter and before material.

Source and disclaimer

All technical data on this page, including standards, test conditions, materials, hardness values, corrosion resistance, temperature ranges, size ranges, torque figures and clamp load figures, is taken from the LNA Solutions Wedge Washer print catalog. Torque and clamp load values are guidelines only. Each critical bolted joint should be analyzed individually by a design engineer. Certifications and approvals are product-specific and should be confirmed for your application. For project-specific values, contact our engineering team.

Last reviewed: September 11, 2026