What is the difference between ISO 7089 and ISO 7090?

ISO 7089 is a plain (flat) washer, normal series, 200 HV hardness. ISO 7090 is the same dimensions but with a chamfer on one side (beveled edge), also 200 HV. ISO 7090 prevents the washer from digging into soft surfaces.

What size washer do I need for an M10 bolt?

For an M10 bolt per ISO 7089: inner diameter 10.5 mm, outer diameter 20 mm, thickness 2.0 mm.

When should I use spring washers?

Spring washers (split lock washers, DIN 127 / ISO 7091) were historically used to prevent loosening. Modern practice prefers Nord-Lock washers, Belleville washers, or chemical threadlockers. Spring washers are now considered less effective than these alternatives.

What hardness should flat washers have?

ISO 7089/7090 specifies 200 HV minimum hardness for standard flat washers. For high-strength bolting (class 10.9/12.9), use washers per ISO 7089 with 300 HV hardness to prevent embedding.

Do I always need a washer under a bolt head?

Washers are recommended when: (1) the hole is oversized, (2) the surface is soft or painted, (3) high-strength bolts are used (prevents embedding), (4) the surface is uneven, or (5) the bolt passes through a slotted hole.

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Washer Selection — ISO 7089 / 7090

Look up flat and spring washer dimensions per ISO 7089/7090 and DIN 127. Select bolt size to view washer ID, OD, and thickness.

ISO 7089ISO 7090DIN 127

Results

Flat Washer — ISO 7089

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Flat Washer ID

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Flat Washer OD

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Flat Washer Thickness

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Spring Washer (DIN 127)

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Flat Washers — ISO 7089 (Normal Series)

Bolt	ID (mm)	OD (mm)	t (mm)
M6	6.4	12	1.6
M8	8.4	16	1.6
M10	10.5	20	2.0
M12	13.0	24	2.5
M16	17.0	30	3.0
M20	21.0	37	3.0
M24	25.0	44	4.0

Washer Selection — ISO 7089/7090 Lookup | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Results

Flat Washers — ISO 7089 (Normal Series)