When we think about engineering failures, we often picture massive structural breaks or dramatic engine meltdowns. But more often than not, catastrophic failures start with something incredibly small: a single nut or bolt backing off due to constant vibration.

While standard flat washers are great for distributing weight, they do very little to stop a fastener from spinning free under stress. That is where internal shakeproof washers (often called internal tooth or serrated lock washers) come into play.

Here is a breakdown of how these small components provide maximum security, why their internal design matters, and where they are best utilized.

How Internal Shakeproof Washers Work

Unlike standard hardware, an internal shakeproof washer relies on mechanical tension and physical friction.

• The Tooth Design: The inner rim of the washer features a series of twisted, sharp prongs or teeth.
• The Bite: As you tighten a nut or bolt down onto the washer, these teeth flatten under the pressure.
• The Lock: The spring tension forces the sharp edges of the teeth to bite directly into the underside of the fastener head and the mating surface. If vibrations try to back the bolt out, the angled teeth dig deeper, preventing rotation.