Metric Washers

What Are Metric Washers?

A metric washer is a flat component installed between a fastener and the surface it's tightened against. Metric washers are sized to metric standards (DIN, ISO, and related specifications) for use with metric bolts, screws, and nuts used throughout international and domestic equipment builds.
Washers spread clamping force over a wider area. They can reduce the risk of surface damage, compensate for oversized clearance holes, and in the case of lock washers, add resistance against loosening from vibration or repeated movement. Different applications call for different washer styles, and choosing the right one affects how well the whole assembly holds up over time.

Types of Metric Washers

Flat Washers

Metric flat washers are the standard round, flat washer used under most bolted connections. Their primary job is load distribution: spreading the clamping force of the fastener across a broader surface area so the base material doesn't dent, crack, or wear unevenly. Our stock includes:

• DIN 125A, in plain, zinc CR+3, zinc-yellow CR+6, A2 stainless, and hardened 140 Hv / 200 Hv
• DIN 433 small flat washers
• DIN 7349 thick flat washers
• F436M hardened flat washers
• ASME B18.22M narrow, in thru-hardened and A2 stainless

Fender Washers

Fender washers use the same flat shape with a much larger outside diameter, giving extra coverage for oversized or irregular holes and thin or soft base materials. In stock:

• DIN 9021B, Grade A, zinc CR+3
• DIN 9021B, Grade C, zinc CR+3

Split Lock Washers

Also called helical spring lock washers, these are coiled and split rather than flat. As the fastener tightens, the washer compresses and stores spring tension against the joint, resisting the backing-off that vibration and repeated stress can cause. In stock:

• DIN 127B, A2 stainless steel
• DIN 127B, thru-hardened plain
• DIN 127B, thru-hardened zinc/blue CR+3
• DIN 127B, zinc-yellow CR+6

External Tooth Lock Washers

Teeth on the outer edge bite into the mating surface as the fastener tightens. Because the teeth engage at a larger diameter, these generally resist rotation better than internal tooth designs, and they pair well with larger fastener heads on machine guards, brackets, and cable clamps. In stock:

• DIN 6797A, zinc CR+3
• DIN 6798A, serrated, zinc CR+3

Internal Tooth Lock Washers

Same biting principle, but the teeth sit on the inner diameter and grip beneath the fastener head. That keeps the washer mostly hidden once installed, a good fit for grounding points, control panels, and compact assemblies. In stock:

• DIN 6797J, zinc CR+3

Hi-Collar Lock Washers

A split lock washer variant with a smaller outside diameter and taller profile, built to fit under socket head cap screws and into counterbored holes where a standard split lock washer won't clear. The added thickness keeps locking force intact despite the smaller footprint. In stock:

• DIN 7980, plain finish

Metric Washer Grades and Materials

• Low carbon and thru-hardened steel for general-purpose and higher-strength bolt and screw assemblies, including 140 Hv and 200 Hv hardened flat washers
• A2 stainless steel for corrosion resistance
• Zinc CR+3 and zinc-yellow CR+6 finishes for moderate corrosion protection at a lower cost than stainless
• Plain and zinc/blue CR+3 finishes on select thru-hardened parts where a lower-cost coating is preferred
• Lock washer styles (split, external tooth, internal tooth, and hi-collar) engineered specifically to resist loosening in equipment exposed to vibration

Common Metric Washer Applications

• Machinery and machine tooling
• General equipment assembly
• Automotive components
• Construction and structural applications
• Electrical assemblies
• Industrial maintenance
• Applications exposed to vibration or movement

Frequently Asked Questions

What are metric washers used for?

Metric washers distribute clamping load across a wider surface area, protect the base material from damage, and help fill oversized or irregular clearance holes. Lock washers help resist loosening caused by vibration.

What is the difference between flat washers and lock washers?

Flat washers are smooth and flat, and their main function is spreading load and protecting surfaces. Lock washers, whether split or tooth style, are designed to add resistance against a fastener backing off once it's tightened. Use a flat washer for general load distribution and a lock washer when the assembly will see vibration or repeated stress.

When should I use fender washers?

Fender washers make sense when a bolt passes through an oversized or irregular hole, or when you're fastening into thin or soft material that needs extra surface coverage to avoid cracking or pulling through.

What is the difference between split lock washers and tooth lock washers?

Split lock washers use spring tension from a split ring to resist loosening. Tooth lock washers, whether internal or external, use small teeth that physically bite into the mating surface for a mechanical grip.

What are hi-collar lock washers used for?

Hi-collar lock washers are built for socket head cap screws and other applications with limited clearance. Their smaller outside diameter fits into counterbored holes where a standard split lock washer wouldn't clear, while their taller profile keeps the locking force effective.

Need Help Finding the Right Metric Washer?

RC Fastener stocks metric flat washers, metric lock washers, and specialty styles for machinery, automotive, construction, electrical, and industrial maintenance applications. If you don't see the exact washer you need, send us a quick quote and we'll help track it down or source it.
Looking for related capabilities? Check out the industries we serve, our custom fastener supply services, or learn more about our quality standards.