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Washers · GB/T 858

M18 Plain Washer Dimensions & Specifications

M18 Plain Washer Dimensions & Specifications reference image

M18 is one of the standard coarse-thread sizes for plain washer under GB/T 858. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.

M18 Dimensional Row (GB/T 858)

For bolt sizeInner diameter d1 (mm)Outer diameter d2 (mm)Thickness t (mm)Reference standard
M1819.034.03.0ISO 7089 / GB/T 97.1

Spanner & Drive for M18 Plain Washer — GB/T 858 (Series 071)

Drive geometry for M18 Plain Washer — GB/T 858 (Series 071) is given by the row above; match the tool to the listed values.

Common Applications for M18 Plain Washer — GB/T 858 (Series 071)

M18 Plain Washer — GB/T 858 (Series 071) are commonly specified for high-load load-spreading on structural joints.

Installation Tips for M18 Plain Washer — GB/T 858 (Series 071)

  • At M18 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 M18

A M18 flat washer pairs with a M18 bolt/screw and matching M18 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 858)

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

Which washer dimensions matter most for M18?

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.

What is the coarse-thread pitch of M18 for Plain Washer — GB/T 858 (Series 071)?

For M18 the standard coarse pitch is 2.5 mm — this is the value used for Plain Washer — GB/T 858 (Series 071).

What clearance and tapping drill suit M18?

Use a 20 mm clearance hole (ISO 273 medium) for through-fixing, or a 15.5 mm tapping drill for a coarse M18 thread.

Should M18 Plain Washer — GB/T 858 (Series 071) be tightened by torque or by angle?

For critical structural joints at M18, angle-controlled or stretch-controlled tightening is more repeatable than pure torque — the friction scatter at large diameters can dominate the torque signal.

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.