A tab washer is a positive-locking device designed to mechanically lock a nut or bolt firmly in place. Unlike shakeproof washers that rely on friction and teeth biting into surfaces, a tab washer creates a physical, unyielding barrier by having its tabs manually bent flat against the flat sides of a fastener head and the mounting structure.
How the Locking Mechanism Works
The Anchor Point: One tab is bent downwards over the edge of the component casing, or fits directly into a pre-drilled locating hole/keyway. This prevents the washer itself from turning.
The Fastener Lock: Once the nut or bolt is torqued down, another tab is forced upward using a chisel or pliers and flattened tightly against one of the flat sides of the hex head.
The Result: The fastener is physically immobilized. It cannot rotate or back off, even under severe harmonic vibrations or impact loads.
Major Types and Variations
Single Tab Washers
Design: Features a single long protruding arm extending from the outer ring.
Application: The long tab is bent over the straight, structural edge of the mounting surface.
Double / Twin Tab Washers
Design: Features two tabs positioned either at a 90-degree or 180-degree offset from each other.
Application: Provides flexibility when locking two separate fasteners positioned close together, or offers alternative angles to bend around oddly shaped components.
Internal / Keyed Tab Washers
Design: Features a small square or rectangular tab extending inward into the central hole.
Application: Slides down a shaft that has a matching machined keyway slot. This anchors the washer to the rotating shaft without needing an external edge to bend against.
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