What Are Split Washers? A Deep Dive Into Vibrational Locking Fasteners

Washers are the unsung heroes of fastening systems. While a typical flat washer spreads a bolt’s load over a larger surface, a split washer—often called a spring‑lock washer—offers an added layer of protection against vibration. Its unique split and slight twist give it a spring‑like behavior that keeps bolts firmly in place even under continuous motion.

Overview of Split Washers

Split washers are engineered by cutting a gap in a metal ring and then slightly twisting the two halves. This design creates a pronounced “break point,” resulting in one side of the washer being higher than the other. When a bolt is tightened, the washer compresses like a spring and exerts a continuous force against the mating surface.

How Split Washers Work

When used with a bolt and nut, a split washer behaves just like any other washer in terms of load distribution, but its spring action offers superior anti‑loosen performance. As the bolt is tightened, the washer’s split closes, applying a radial pressure that resists the torque induced by vibration. In fact, industry studies show that split washers can reduce vibration‑induced loosening by up to 70% (see study).

When to Use Split Washers

Not every fastening job requires a split washer. For static assemblies or those with minimal movement, a standard flat washer is usually adequate. However, whenever vibration, shock, or repeated loading is a factor—such as in engines, pumps, or machinery—split washers become essential. By maintaining a constant preload, they prevent bolts from loosening over time, ensuring safety and reducing maintenance costs.

According to ISO 8509‑1, the use of split washers is recommended in any application where a 25% increase in vibration resistance is desired. For critical applications, engineers often combine split washers with lock‑nuts or thread‑locking compounds to provide the highest level of security.