Pre-Assembled Screw and External-Tooth Washer
The external-tooth washer is installed and retained on the screw during production, eliminating the need to prepare or position the washer separately during assembly. This helps reduce assembly steps and improve efficiency in both manual and high-volume production.
External Teeth Provide Auxiliary Anti-Loosening Performance
After tightening, the teeth of the external-tooth washer deform elastically and engage with the underside of the screw head and the mating surface of the workpiece. This increases frictional resistance at the contact area and helps reduce rotational loosening under general vibration conditions.
Actual anti-loosening performance should still be evaluated according to tightening torque, workpiece material, surface hardness, applied load, and vibration level.
Wider Tooth Engagement Area
Because the teeth are distributed around the outer edge of the washer, the engagement area is generally wider than that of an internal-tooth washer. This provides more gripping points with the workpiece and is suitable for applications with larger screw heads or wider contact surfaces.
Helps Maintain Metal-to-Metal Contact
When tightened, the external teeth can bite into the metal surface. Under certain assembly conditions, this may help penetrate thin oxide films, paint, or surface coatings and improve the stability of metal-to-metal contact.
For products with grounding, electrical conductivity, or electromagnetic compatibility requirements, actual testing should still be performed to confirm contact resistance and electrical continuity. Washer structure alone should not be used as the sole basis for determining electrical performance.
Reduces the Risk of Missing or Dropped Washers
Because the washer is retained on the screw, it helps reduce missing washers, dropped parts, size mix-ups, or installation errors during manual assembly. This supports greater assembly consistency in high-volume production.
Improves Production-Line Assembly Efficiency
Operators only need to handle one complete fastener assembly and do not need to pick up the screw and washer separately. This reduces handling steps and helps shorten assembly time.
Suitable for Automated Feeding and Fastening
The pre-assembled structure helps reduce problems such as loose washers overlapping, jamming, falling off, or becoming incorrectly oriented in vibratory bowls, feeding tracks, or automatic fastening equipment, making it suitable for automated assembly.
Actual feeding stability should still be tested according to the screw head type, screw length, washer outside diameter, and equipment specifications.
Simplifies Purchasing and Inventory Management
Integrating the screw and external-tooth washer into a single part number can reduce the number of items that need to be managed during purchasing, receiving, material issuing, and production-line preparation. This helps lower the risk of shortages or incorrect specification matching.
Multiple Screw Specifications Available
Different screw head types, drive styles, thread specifications, lengths, and external-tooth washer dimensions can be selected according to assembly tools, available installation space, workpiece material, and fastening requirements.
Customization Based on Drawings and Samples
W/EXT.WAS. products can be customized according to customer engineering drawings or physical samples, including screw head type, drive type, thread diameter, thread pitch, length, washer inner and outside diameters, number and profile of teeth, materials, tolerances, and surface treatments.
Common Applications
W/EXT.WAS. is commonly used in:
- Electronic and electrical equipment
- Electrical panels, control boxes, and metal cabinets
- Telecommunications and information equipment
- Machinery and automation equipment
- Automotive and motorcycle components
- Home appliances and consumer products
- Instruments and precision equipment
- Sheet metal, enclosures, and metal housings
- Assembly locations requiring auxiliary anti-loosening or metal-to-metal contact
- Mass-production and automated fastening lines
Key Considerations When Selecting W/EXT.WAS.
Before selection, confirm the screw thread diameter, thread pitch, length, head type, and drive type. The inner diameter, outside diameter, number of teeth, and thickness of the external-tooth washer should also be checked against the available installation space.
Because the external teeth extend beyond the main body of the washer, sufficient contact area and surrounding clearance must be provided. If nearby components are closely spaced, or if the installation area contains flanges, grooves, or other interfering structures, the washer outside diameter and tooth dimensions should be confirmed in advance.
External-tooth washers may leave tooth marks on the workpiece surface and can scratch paint, plating, or other surface finishes. If the product requires a high-quality appearance, sealing performance, or corrosion protection, the effect of the teeth on the contact surface should be evaluated in advance.
External-tooth washers are an auxiliary anti-loosening feature. For applications involving severe vibration, repeated impact, or safety-critical equipment, they should not be relied upon as the sole locking method. Thread-locking compounds, lock nuts, or other mechanical locking methods should also be evaluated.
After repeated assembly and disassembly, the teeth should be inspected for flattening, wear, breakage, or loss of elasticity. If the teeth can no longer effectively engage the mating surface, replacement with a new component is recommended.
