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Slotted Flat Washer Spring

Updated: 2026-07-22

Overview

The split washer spring is a fundamental anti-loosening fastener widely used in mechanical assemblies. Its split-ring design creates a spring action that maintains tension between bolted components, counteracting vibrational loosening. First patented in the early 20th century, it remains a cost-effective solution for medium-duty applications. Standardized under DIN 127 (metric) and ANSI B18.21.1 (imperial), these washers are manufactured through precision stamping and heat treatment processes. While traditional designs use high-carbon steel, modern variants include stainless steel (A2/A4 grades) for corrosive environments and non-magnetic applications.

Structure and Working Principle

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The washer's effectiveness stems from its simple yet ingenious geometry. The split in the ring allows elastic deformation when compressed, generating a restoring force that keeps the fastener under tension. The sharp edges at the split ends bite slightly into both the bolt head/nut and the mating surface, creating additional resistance to rotation. Under load, the washer flattens to about 60–70% of its original height, maintaining consistent pressure even after material creep or settling occurs. The spring rate (force per unit deflection) depends on material thickness and the washer's outer diameter to thickness ratio, with standard designs offering 5–15 N/mm spring rates.

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Key Features

Split washers provide three primary functional benefits: vibrational resistance through spring tension, surface bite action for rotational resistance, and compensation for thermal expansion differences in assemblies. High-carbon steel variants typically offer 42–60 HRC hardness after heat treatment, ensuring durability under repeated compression cycles. Specialized versions include external tooth lock washers for softer materials and serrated designs for enhanced grip. Temperature resistance ranges from -30°C to +250°C for standard steel washers, with stainless steel variants maintaining performance up to 400°C. Electrically conductive versions are available for grounding applications in electrical panels.

Application Areas

These washers see ubiquitous use across industries where vibration is a concern. Automotive applications include engine mounts, exhaust systems, and wheel assemblies. Industrial machinery employs them in motor mounts, gearbox covers, and conveyor systems. They're also standard in construction equipment, agricultural machinery, and HVAC systems. While effective for general-purpose use, they're not recommended for critical aerospace or high-vibration marine applications where prevailing torque nuts or thread-locking compounds are preferred. Proper usage requires adequate bearing surface area—typically 1.5 times the washer diameter—to prevent surface deformation.

Maintenance and Precautions

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Inspection should check for loss of spring tension (flattening beyond 80% compression) or visible cracks at the split ends—both indicate replacement is needed. Reuse is generally discouraged as work hardening reduces elasticity. Galvanic corrosion can occur when dissimilar metals are used; insulating washers may be required in such cases. Installation requires the split side to face the nut/bolt head (not the joint surface) for optimal bite action. Over-tightening beyond the washer's elastic limit can cause permanent deformation, negating its locking function. For high-vibration environments, pairing with a flat washer (DIN 125) beneath the split washer distributes load more evenly.

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B2B Procurement Guide

Bulk purchasing typically follows nominal diameter specifications (e.g., M6, 1/4"). Reputable manufacturers provide material certifications (e.g., ASTM F436 for hardened steel) and salt spray test reports for corrosion-resistant grades. MOQs commonly start at 10,000 pieces for standard sizes, with lead times of 2–4 weeks for customized coatings or materials. Quality indicators include consistent hardness (Rockwell C testing), clean stamping edges without burrs, and proper heat treatment (evidenced by blue tempering colors). For specialized applications, consult technical datasheets for fatigue life cycles—quality washers should withstand ≥50,000 vibration cycles without failure. Tier 1 automotive suppliers often require PPAP documentation for approved vendor lists.

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