M18 Washer Dimensions & Size
The M18 size is available in three specialized series: the Normal Series (DIN 125A / ISO 7089) for standard load distribution, the Large Series (DIN 9021 / ISO 7093) for a massive increase in surface area, and the Small Series (DIN 433 / ISO 7092) for applications where radial space is highly restricted. Based on these standards, M18 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 extreme clamping forces 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. Zinc-Plated Steel) and manufacturing class. Always verify with the official product datasheet for critical applications.
| M18 Standard Series Washer – DIN 125A/ISO 7089 | ||
|---|---|---|
| Dimension | Size (mm) | |
| Min | Max | |
| Inner Diameter | 19 | 19.33 |
| Outside Diameter | 33.38 | 34 |
| Thickness | 2.7 | 3.3 |
| M18 Large Series Washer – DIN 9021/ISO 7093 | ||
|---|---|---|
| Dimension | Size (mm) | |
| Min | Max | |
| Inner Diameter | 20 | 20.52 |
| Outside Diameter | 54.1 | 56 |
| Thickness | 3.4 | 4.6 |
| M18 Small Series Washer – DIN 433/ISO 7092 | ||
|---|---|---|
| Dimension | Size (mm) | |
| Min | Max | |
| Inner Diameter | 19 | 19.33 |
| Outside Diameter | 29.48 | 30 |
| Thickness | 2.3 | 2.7 |
- 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 “M18” designation mean on a washer?
The “M” stands for Metric, and the number represents the nominal thread diameter of the screw or bolt. An M18 washer is designed specifically for fasteners with an 18 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) M18 washer?
The Large Series (DIN 9021 / ISO 7093) features an exceptionally wide outside diameter of 56 mm. It is used when fastening into softer materials like structural timber, composites, or oversized holes in heavy plating, where the clamping force must be spread over the largest possible area to prevent surface crushing or pull-through.
What does the HV rating mean on a washer?
HV stands for Vickers Hardness. For M18 fasteners, a rating of 200 HV or 300 HV is standard for steel and stainless steel. This ensures the washer maintains its flatness and resists indentation even when subjected to the high torque levels required for heavy mechanical joints.
What is the difference between Small Series (DIN 433) and Normal Series?
The Small Series (DIN 433 / ISO 7092) has a narrower outside diameter (30 mm) compared to the Normal Series (34 mm). It is specifically intended for use with Socket Head Cap Screws or in recessed counterbores where a standard-width washer would be too large to fit the available housing.
In which materials are M18 washers commonly available?
M18 washers are most frequently produced in A2 (304) and A4 (316) Stainless Steel for corrosion resistance. They are also widely available in Hot-Dip Galvanized Steel for outdoor construction and Zinc-Plated Steel for general industrial hardware.