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Washers · GB/T 95 / ISO 7091

M20 Flat Plain Washer Dimensions & Specifications

M20 Flat Plain Washer Dimensions & Specifications reference image

M20 is one of the standard coarse-thread sizes for flat plain washer under GB/T 95 / ISO 7091. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.

M20 Dimensional Row (GB/T 95 / ISO 7091)

For bolt sizeInner diameter d1 (mm)Outer diameter d2 (mm)Thickness t (mm)Reference standard
M2021.037.03.0ISO 7089 / GB/T 97.1

Spanner & Drive for M20 Flat Plain Washer — GB/T 95 / ISO 7091 (Series 079)

Drive geometry for M20 Flat Plain Washer — GB/T 95 / ISO 7091 (Series 079) is given by the row above; match the tool to the listed values.

Common Applications for M20 Flat Plain Washer — GB/T 95 / ISO 7091 (Series 079)

M20 Flat Plain Washer — GB/T 95 / ISO 7091 (Series 079) are commonly specified for high-load load-spreading on structural joints.

Installation Tips for M20 Flat Plain Washer — GB/T 95 / ISO 7091 (Series 079)

  • At M20 the stretch in the bolt becomes the controlling factor — for critical joints, use angle-controlled or stretch-controlled tightening instead of pure torque.

Mating Parts for M20

A M20 flat washer pairs with a M20 bolt/screw and matching M20 nut.

Technical Drawing

Customize the parameters below — every spec field is editable, and the drawing redraws to match the values you choose. Changing the size will snap the other fields to that size's standard values; you can then override any individual value.

Sends the selected values to the quote form below.

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Adjust the parameters in the drawing above and click "Request this configuration" to send the exact specification straight to this form.

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Specification
Business Information

Dimensions & Specifications (GB/T 95 / ISO 7091)

For bolt sizeInner diameter d1 (mm)Outer diameter d2 (mm)Thickness t (mm)Reference standard
M33.27.00.5ISO 7089 / GB/T 97.1
M44.39.00.8ISO 7089 / GB/T 97.1
M55.310.01.0ISO 7089 / GB/T 97.1
M66.412.01.6ISO 7089 / GB/T 97.1
M88.416.01.6ISO 7089 / GB/T 97.1
M1010.520.02.0ISO 7089 / GB/T 97.1
M1213.024.02.5ISO 7089 / GB/T 97.1
M1415.028.02.5ISO 7089 / GB/T 97.1
M1617.030.03.0ISO 7089 / GB/T 97.1
M1819.034.03.0ISO 7089 / GB/T 97.1
M2021.037.03.0ISO 7089 / GB/T 97.1
M2425.044.04.0ISO 7089 / GB/T 97.1
M3031.056.04.0ISO 7089 / GB/T 97.1
M3637.066.05.0ISO 7089 / GB/T 97.1

Frequently Asked Questions

What clearance and tapping drill suit M20?

Use a 22 mm clearance hole (ISO 273 medium) for through-fixing, or a 17.5 mm tapping drill for a coarse M20 thread.

Should M20 Flat Plain Washer — GB/T 95 / ISO 7091 (Series 079) be tightened by torque or by angle?

For critical structural joints at M20, angle-controlled or stretch-controlled tightening is more repeatable than pure torque — the friction scatter at large diameters can dominate the torque signal.

What grip range is typical for M20 structural bolts?

Grip ranges are highly application-dependent at M20. As a guide, choose a length that gives at least 1× the thread diameter engagement in the nut plus 2–3 thread pitches projecting.

Which washer dimensions matter most for M20?

For a flat washer, the outside diameter (the bearing surface) and the thickness control how the load is spread under the head and how much elastic preload is preserved. The inside diameter must clear the bolt body but not be so large that the head bears mostly on the washer's outer rim.

How do I request a quotation?

Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.