Overview
Internal tooth lock washers are precision-engineered fasteners designed to maintain tension in bolted joints subjected to vibration or thermal cycling. Unlike flat washers, their internal teeth dig into both the fastener and the workpiece, creating a locking action. They are a cost-effective alternative to thread-locking adhesives in medium-duty applications. First patented in the early 20th century, these washers evolved from split washers (helical spring washers) to provide more consistent locking force. Modern versions comply with international standards like DIN 6797 (Germany) and JIS B 1251 (Japan), ensuring interchangeability across global supply chains.
Structure and Working Principle
The washer’s design features a flat ring with radially inward-pointing teeth. When compressed between a bolt/nut and the workpiece, the hardened teeth deform slightly to embed into both surfaces. This creates three anti-loosening effects: elastic tension from the compressed washer, friction from the tooth contact, and mechanical interference from the tooth indentations. Tooth geometry varies by application—coarse teeth (6–12 teeth) suit heavier loads, while fine teeth (16–24 teeth) work better for smaller fasteners. High-quality washers undergo heat treatment to achieve 42–50 HRC hardness, balancing bite capability with material toughness.
Key Features
Material selection directly impacts performance. Spring steel (SAE 1074/1095) offers optimal elasticity and bite strength for most industrial uses, while stainless steel variants (AISI 304/316) provide corrosion resistance at slightly higher cost. Carbon steel washers are economical but require plating for rust prevention. Advanced versions may include nylon coatings to reduce galvanic corrosion or combined tooth/external wave designs for extreme vibration environments. Testing by the Fastener Testing Foundation confirms properly installed internal tooth washers can withstand 5,000+ vibration cycles without loosening.
Application Areas
These washers are indispensable in automotive subassemblies (engine mounts, exhaust systems), agricultural machinery (harvester joints), and electrical enclosures subject to electromagnetic vibration. They outperform split washers in applications with frequent thermal expansion, such as HVAC ducting. In electronics manufacturing, miniature internal tooth washers (M2–M6 sizes) secure critical components on printed circuit boards. Offshore applications often specify stainless steel versions to resist saltwater corrosion. For aerospace, special alloys like Inconel may be used for high-temperature resistance.
Maintenance and Precautions
Unlike reusable fasteners, internal tooth washers should be replaced after disassembly because the teeth lose their sharpness and locking effectiveness. During installation, ensure the washer sits flat without cross-threading the teeth. Over-tightening can shear teeth, while under-tightening reduces friction. Inspect washers for proper hardness by verifying they can’t be easily bent by hand. For soft substrates like plastic or cast aluminum, consider flange bolts or shoulder washers to prevent material damage. Always pair with hardened bolts (grade 8.8 or higher) to ensure the teeth bite effectively.
B2B Procurement Guide
Bulk buyers should specify material grade, hardness, tooth count, and compliance standards (e.g., DIN 6797 Type A). For high-volume orders (50,000+ units), Chinese manufacturers offer competitive pricing at $0.02–$0.10 per piece, while European/US suppliers charge $0.15–$0.50 for premium certifications. Quality checks should include salt spray testing (72+ hours for zinc-plated versions) and batch hardness testing. Lead times vary from 2 weeks (stock items) to 8 weeks (custom alloys). Consider kitting services where washers are pre-sorted with matching bolts/nuts to streamline assembly lines.
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