M4 Washer Dimensions & Size

M4 washer dimensions are standardized for a wide variety of engineering applications, including computer chassis assembly, automotive interior trim, consumer appliances, and mechanical mounting systems. Specifically designed for fasteners with a 4 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 M4 size is a versatile industrial standard available in three 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. Based on these standards, M4 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
M4 Standard Series Washer – DIN 125A/ISO 7089
Dimension Size (mm)
Min Max
Inner Diameter 4.3 4.48
Outside Diameter 8.64 9
Thickness 0.7 0.9
M4 Large Series Washer – DIN 9021/ISO 7093
Dimension Size (mm)
Min Max
Inner Diameter 4.3 4.48
Outside Diameter 11.57 12
Thickness 0.9 1.1
M4 Small Series Washer – DIN 433/ISO 7092
Dimension Size (mm)
Min Max
Inner Diameter 4.3 4.48
Outside Diameter 7.64 8
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 “M4” designation mean on a washer?

The “M” stands for Metric, and the number represents the nominal thread diameter of the screw or bolt. An M4 washer is designed specifically for fasteners with a 4 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) M4 washer?

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

What does the HV rating mean on a washer?

HV stands for Vickers Hardness. For M4 fasteners, a rating of 200 HV or 300 HV is standard for steel and stainless steel, ensuring the washer maintains its flatness and resists deformation when tightened to the 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) has a narrower outside diameter compared to the Normal Series (DIN 125A / ISO 7089). It is designed for use in recessed holes or on densely packed components where a standard washer might overlap or interfere with neighboring parts.

In which materials are M4 washers commonly available?

M4 washers are most frequently produced in A2 (304) and A4 (316) Stainless Steel for corrosion resistance. They are also widely available in Zinc-Plated Steel for general-purpose hardware and Nylon 66 for electrical insulation.