TOOTH WASHER

"Tooth washers" are formally known as toothed lock washers or shakeproof washers, and are widely available in a zinc-plated finish for corrosion resistance. They are designed to prevent fasteners from loosening due to vibration by "biting" into the mating surface. 

Types of Zinc Toothed Lock Washers
Zinc-plated toothed lock washers come in various configurations, primarily internal and external designs, to suit different application needs. 

Internal Tooth Lock Washers
Description: These washers have teeth along the inner circumference.
Aesthetics: The teeth are hidden under the screw head or nut, providing a cleaner, more aesthetically pleasing appearance.
Application: Best used with small screw heads and for electrical ground bonding connections, where the teeth cut through paint or surface oxides to make a better electrical connection.
Corrosion Protection: The zinc plating offers an average level of corrosion protection, making them suitable for internal applications.

External Tooth Lock Washers
Description: These washers feature teeth that extend radially outward from the outer diameter.
Performance: The external tooth design provides greater twisting resistance and superior anti-loosening security because the teeth grip the surface at a larger radius.
Application: Ideal for use in high-vibration environments and with larger-headed screws (like pan or round heads).
Corrosion Protection: They are typically bright zinc plated (BZP) for corrosion resistance. 

Key Features of Zinc Finish
The zinc finish (applied via electroplating or mechanical means) is a popular choice due to its balance of cost and performance. 
Corrosion Resistance: The zinc coating acts as a sacrificial barrier, protecting the steel material underneath from moisture, oxidation, and mild chemicals.
Aesthetics: It provides a smooth, bright silver appearance.
Durability: The finish enhances surface hardness, boosting the overall durability and wear resistance of the washer.