Stainless Steel Tooth Washer

Choosing the Right Tooth Washer

(Serrated / Toothed Lock Washer – Internal & External Tooth)

1) What does a tooth washer do & when should you use it?

A tooth washer (also called toothed / serrated lock washer) is a thin washer with multiple teeth formed on its inner or outer edge. It is designed to:

Bite into the nut/bolt and the mating surface

Increase friction and resistance to loosening

Provide a small spring effect

In many cases, break through paint/oxide for better electrical contact

Use a tooth washer when:

You need better anti-rotation than a plain washer alone

Fasteners are subject to light–moderate vibration

You need good electrical bonding/earthing across painted or plated surfaces (panels, lugs, terminals)

2) Types of tooth washers – which one to choose?

The main common types for your catalogue:

a) Internal Tooth Washer

Teeth are on the inner diameter.

Best under small screw heads (pan, cheese, round) and for electrical terminals.

Keeps the outer profile smooth, useful in tight spaces.

Use for:

Electrical lugs, terminal strips, PCB hardware, control panels

Small screws where space around the head is limited

b) External Tooth Washer

Teeth are on the outer diameter.

Gives a larger OD and generally stronger locking action (larger lever arm).

Ideal under hex bolt heads and nuts on flat plates.

Use for:

Nuts and hex bolts in light–medium duty joints

Brackets, small frames, enclosures where you want higher bite into the surface

c) Serrated / Conical Tooth Washer (if you stock them)

A slightly conical washer with serrations on one or both faces.

Combines spring action with biting serrations.

Used where you want both elastic preload and high friction.

Use for:

Joints needing better vibration resistance than a plain washer plus basic spring washer

Compact mechanical assemblies

3) Environment & corrosion – choosing material & finish

Indoor / dry / general electrical & mechanical use:

MS tooth washers (mild steel)

Zinc-plated or black/phosphated finishes.

Common in electrical panels, appliances, general machinery, enclosures.

Outdoor / mild industrial environments:

Zinc-plated MS tooth washers for moderate protection.

For more demanding conditions, prefer stainless.

Stainless / food / pharma / marine / chemical conditions:

SS 304 (A2) tooth washer

For general outdoor, food-grade, and stainless assemblies.

SS 316 (A4) tooth washer

For marine, coastal, and chemical exposure.

Best for harsh environments and hygienic applications.

Best practice:
Always try to match washer material with the bolt/nut material and environment to reduce galvanic corrosion and staining.

Mechanical Properties (Guide) – Tooth Washer

Tooth washers are thin locking components, not structural load carriers. Key properties are material, hardness, and the spring/biting behaviour of the teeth.

1) Mild steel tooth washers (standard)

Typical characteristics:

Material: low/medium carbon steel often hardened or work-hardened at the edges.

Thicker than simple shim stock, but still relatively thin compared to structural washers.

Functional behaviour:

Teeth deflect slightly under tightening torque, providing small spring effect.

During tightening, tooth tips embed into:

The underside of the screw/bolt head or nut

The joint member surface (panel, lug, bracket)

This:

Increases interface friction and resistance to rotation.

Helps maintain good metal-to-metal contact, useful for grounding.

Limitations:

Over-tightening can flatten the teeth, reducing their locking ability.

They are not intended to carry high bearing pressure like thick structural washers.

2) Stainless tooth washers (A2 / A4)

Typical characteristics:

Material: A2 (304) or A4 (316) stainless steel.

Good combination of corrosion resistance and spring/bite capability.

Functional behaviour:

Similar locking function as carbon steel tooth washers, with better resistance to rust.

Ideal for stainless panels, outdoor boxes, marine gear, and food/pharma machines where both locking and cleanliness/corrosion resistance matter.

Teeth may be slightly less sharp than hardened carbon steel but still provide effective bite in most applications.

3) Behaviour in a bolted joint

In a correctly tightened joint:

Teeth are partially embedded in mating surfaces.

The washer adds elastic reaction + extra friction.

The joint still relies primarily on bolt tension (preload) for overall integrity; the tooth washer mainly improves lock/anti-rotation and electrical contact.

Typical failure/limit conditions:

Flattened or worn teeth if over-torqued or repeatedly reused.

Loss of bite if surfaces are very soft (thick plastic, wood) and deform heavily under tooth pressure.

Insufficient locking under extreme vibration if used alone – additional locking methods may be needed (nylock, thread-locker, etc.).