M3 Washer Dimensions & Size

Q: What does the “M3” designation mean on a washer?

The “M” stands for Metric, and the number represents the nominal thread diameter of the screw or bolt. An M3 washer is designed specifically for fasteners with a 3 mm nominal major diameter.

Q: What is the difference between Form A and Form B washers?

The difference lies in the outer edge finish. Form A washers have a square, flat edge and are the most common. Form B washers include a 30° to 40° chamfer (beveled edge) on one side, according to DIN 125B and ISO 7090 standards.

Q: When should I use a Large Series (DIN 9021) M3 washer?

The Large Series (DIN 9021 / ISO 7093) has a significantly larger outside diameter, approximately three times the nominal thread size. It is used when fastening into soft materials like plastic, thin wood, or sheet metal, where you need to spread the clamping load over a wider surface area to prevent the screw head from pulling through.

Q: What does the HV rating mean on a washer?

HV stands for Vickers Hardness. For M3 fasteners, a rating of 200 HV or 300 HV is standard for steel and stainless steel, ensuring the washer maintains its flatness and structural integrity when tightened to required torque levels in mechanical assemblies.

Q: What is the difference between Small Series (DIN 433) and Normal Series?

The Small Series (DIN 433 / ISO 7092) features a narrower outside diameter compared to the Normal Series (DIN 125A / ISO 7089). It is specifically intended for use where space is limited, such as fitting inside recessed holes or on densely packed circuit boards where a standard washer might overlap other components.

Q: In which materials are M3 washers commonly available?

M3 washers are most frequently produced in A2 (304) and A4 (316) Stainless Steel for corrosion resistance. They are also widely available in Nylon 66 for electrical insulation and Zinc-Plated Steel for general-purpose hardware applications.

M3 washer dimensions are standardized for a wide range of applications, including 3D printing, computer hardware assembly, consumer electronics, and robotics. Specifically designed for fasteners with a 3 mm nominal diameter, these components ensure stable load distribution and protect mating surfaces from damage during tightening. This chart covers Form A plain washers, which feature a flat surface without a chamfer (unlike Form B).

The M3 size is highly versatile and is available in three standardized series: the Normal Series (DIN 125A / ISO 7089) for standard load distribution, the Large Series (DIN 9021 / ISO 7093) for increased surface area, and the Small Series (DIN 433 / ISO 7092) for tight clearances where space is at a premium. Based on these standards, M3 washers typically feature a hardness of 200 HV or 300 HV (Vickers Hardness), providing the structural integrity required to prevent “cupping” or deformation under the clamping force of high-tensile bolts.

Note: While these values reflect standard manufacturer datasheets, actual dimensions and tolerances may vary based on material (e.g., Stainless Steel vs. Nylon) and manufacturing class. Always verify with the official product datasheet for critical applications.

Washer dimension diagram showing inner diameter, outside diameter, and thickness

M3 Standard Series Washer – DIN 125A/ISO 7089
Dimension	Size (mm)
Dimension	Min	Max
Inner Diameter	3.2	3.38
Outside Diameter	6.64	7
Thickness	0.45	0.55

M3 Large Series Washer – DIN 9021/ISO 7093
Dimension	Size (mm)
Dimension	Min	Max
Inner Diameter	3.2	3.38
Outside Diameter	8.64	9
Thickness	0.7	0.9

M3 Small Series Washer – DIN 433/ISO 7092
Dimension	Size (mm)
Dimension	Min	Max
Inner Diameter	3.2	3.38
Outside Diameter	5.7	6
Thickness	0.45	0.55

Inner Diameter – The diameter of the hole, designed to clear the bolt/screw thread.
Outside Diameter – The total width of the washer, determining the load distribution area.
Thickness – The height of the washer, providing the spacing and structural support.

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Frequently Asked Questions

What does the “M3” designation mean on a washer?

The “M” stands for Metric, and the number represents the nominal thread diameter of the screw or bolt. An M3 washer is designed specifically for fasteners with a 3 mm nominal major diameter.

What is the difference between Form A and Form B washers?

The difference lies in the outer edge finish. Form A washers have a square, flat edge and are the most common. Form B washers include a 30° to 40° chamfer (beveled edge) on one side, according to DIN 125B and ISO 7090 standards.

When should I use a Large Series (DIN 9021) M3 washer?

The Large Series (DIN 9021 / ISO 7093) has a significantly larger outside diameter, approximately three times the nominal thread size. It is used when fastening into soft materials like plastic, thin wood, or sheet metal, where you need to spread the clamping load over a wider surface area to prevent the screw head from pulling through.

What does the HV rating mean on a washer?

HV stands for Vickers Hardness. For M3 fasteners, a rating of 200 HV or 300 HV is standard for steel and stainless steel, ensuring the washer maintains its flatness and structural integrity when tightened to required torque levels in mechanical assemblies.

What is the difference between Small Series (DIN 433) and Normal Series?

The Small Series (DIN 433 / ISO 7092) features a narrower outside diameter compared to the Normal Series (DIN 125A / ISO 7089). It is specifically intended for use where space is limited, such as fitting inside recessed holes or on densely packed circuit boards where a standard washer might overlap other components.

In which materials are M3 washers commonly available?

M3 washers are most frequently produced in A2 (304) and A4 (316) Stainless Steel for corrosion resistance. They are also widely available in Nylon 66 for electrical insulation and Zinc-Plated Steel for general-purpose hardware applications.