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Lock washers look simple: a split ring under a bolt head, a toothed edge against a steel plate, or a curved washer compressed into a joint. Yet choosing the right type depends on the joint, materials, vibration, and installation—not appearance alone. The 2024 Grand View Research Fastener Market report valued the global fastener market at about $90.96 billion in 2023. That broad figure shows the scale of fastening applications; it does not measure lock washers separately.
This guide compares common Washer Lock Washer types, including split, internal-tooth, external-tooth, and wedge-lock designs. It will examine where each may suit a joint, what limitations to consider, and why washer choice cannot compensate for poor assembly. NASA’s Fastener Design Manual, authored by Richard T. Barrett, provides technical guidance on fastener selection and joint design. Barrett’s work underscores a practical point: reliable joints require attention to the complete fastening system, not one component in isolation. I could not verify a published, verbatim Barrett quotation specifically about lock washers, so I have not invented one.
There is no universal winner. A toothed washer may grip a surface, but coatings and soft materials can change the result. A split washer may be familiar, yet familiarity is not proof of suitability. The comparisons ahead are a starting point, not a substitute for application-specific engineering review.
What Are the Top Lock Washer Types in 2026?
What Lock Washers Are and How They Resist Loosening
A lock washer sits beneath a nut or bolt head to help maintain a secure joint. Split washers use spring force; toothed washers press their edges into the mating surfaces. Both can help resist rotation, but neither replaces correct bolt preload. Picture a washer beneath a steel bracket: if the joint is poorly tightened, vibration can still loosen it. That matters.
NASA’s Fastener Design Manual, RP-1228, describes torque-controlled preload as having roughly ±25% accuracy, with friction affecting results. This is a useful reminder: a washer cannot correct uneven clamping force. Washer performance also depends on the materials, surface finish, load, and vibration. Split washers, in particular, may not provide reliable protection in every joint. Treat them as one part of a fastening design, not a guarantee.
Tips: Match the washer to the joint and check the assembly guidance. Keep mating surfaces clean, tighten with a calibrated tool, and inspect joints exposed to repeated vibration. When failure matters, verify the design with suitable testing. That extra check is worth it.
| Washer Type | How It Resists Loosening | Common Applications | Main Advantages | Limitations and Installation Notes | Common Materials |
|---|---|---|---|---|---|
| Split (Helical Spring) Lock Washer | The split ring is slightly helical and compresses as the fastener is tightened, creating spring force and localized resistance at the bearing surfaces. | General-purpose bolted assemblies with modest vibration or movement. | Simple, compact, inexpensive, and widely available. | Testing has found that it may provide little resistance to loosening under severe transverse vibration. It can flatten during tightening and is not a substitute for correct preload or a purpose-designed locking method. | Carbon steel, stainless steel, and alloy steel; finishes may include plain, zinc-plated, or other corrosion-protective coatings. |
| Internal-Tooth Lock Washer | Inward-facing teeth grip the fastener head or nut and the bearing surface, adding resistance to rotation. | Small fasteners, confined spaces, and assemblies with relatively small bearing surfaces. | Teeth are largely hidden beneath the fastener, and the washer can fit around a compact head. | Teeth need a surface they can engage. They may mark soft materials or damage paint and protective coatings; effectiveness depends on suitable tightening and contact surfaces. | Hardened carbon steel and stainless steel. |
| External-Tooth Lock Washer | Outward-facing teeth bite into the fastener bearing face and the mating surface to resist rotation. | Assemblies with larger fastener heads or nuts and applications where the washer’s outer edge can be accommodated. | The larger tooth circle can provide strong surface engagement when the mating materials are suitable. | Teeth are exposed and can scratch surfaces, damage coatings, or be unsuitable for soft or fragile materials. Check clearance around the washer. | Hardened carbon steel and stainless steel. |
| Internal-External-Tooth Lock Washer | Teeth on both the inner and outer edges engage the fastener and the supporting surface. | Applications needing tooth engagement at both contact areas, including some electrical and general mechanical assemblies. | Combines inward and outward tooth contact in one washer. | Can mark both bearing surfaces and may not be appropriate where surface damage, coatings, or soft materials are concerns. | Hardened carbon steel and stainless steel. |
| Wedge-Locking Washer Pair | A matched pair uses cams between the washers and serrations on the outer faces. When the fastener attempts to rotate loose, the cam geometry increases bolt tension rather than allowing easy rotation. | High-vibration bolted joints in machinery, vehicles, and structural equipment when the joint design calls for a mechanical locking system. | Designed to resist rotation-induced loosening while maintaining clamping force when correctly selected and installed. | Use the washers as a correctly oriented, matched pair and confirm compatibility with the fastener, joint, and surface. The pair adds height and may not suit every joint. | Hardened steel or stainless steel, selected for the required strength and environment. |
| Tab Lock Washer | A tab is bent against a nut or bolt head, and another tab or feature may locate against the assembly to prevent rotation mechanically. | Specific machinery and serviceable assemblies designed with a suitable locking feature. | Provides a visible, positive mechanical stop rather than relying only on friction. | Requires a compatible design and correct tab bending. Repeated bending can fatigue the tab, so replacement may be needed during servicing. | Ductile steel or stainless steel, chosen to suit the forming and service requirements. |
| Wave Spring Washer | Its wave-shaped profile deflects under compression and supplies spring force that can help accommodate small changes in joint height or preload. | Assemblies needing axial spring action or compensation for small clearances, rather than a dedicated anti-rotation lock. | Provides spring travel in a relatively low-profile form. | It is primarily a spring or preload-compensation washer, not a positive locking device. Do not assume it will prevent loosening under vibration without joint-specific validation. | Spring steel and stainless spring steel. |
Selection note: A lock washer is a component intended to help resist fastener loosening, but performance depends on joint stiffness, fastener preload, materials, surface condition, and vibration. Follow the equipment design and applicable assembly specifications.