Flat washers · Standard (DIN 125, ISO 7089, ASME B18.21.1, ASTM F436 hardened), size range, material and hardness, finish, and when structural bolting rules require hardened, beveled or plate washers
A flat washer is a thin plate with a central hole placed under a bolt head or nut to spread the clamping load, protect the joint surface and, in hardened form, give a hard bearing face for pretensioned structural bolts. Ask three things first: which standard and size the joint calls for, whether a plain or hardened washer is required, and which material and finish suit the bolt and environment.
Plain and hardened flat washers to DIN, ISO, ASME and ASTM standards, including large (fender) and structural F436 washers, beveled and plate washers. Spring, lock, tooth and sealing washers and rubber gaskets are outside this page except where compared.
CNFX editorial research · Sources checked October 11, 2026 · 4 sources
BSC lists flat washers to DIN 125-A, DIN 126, DIN 9021, ISO 7089 to 7094, ISO 8738, ISO 10669 and 10673, ASME B18.21.1 Type A and Type B, and hardened ASTM F436 flat washers, alongside lock and tooth washers; for DIN 125-A it gives tolerance to DIN 522, steel or stainless steel, and finish to DIN 50979. [2]
Gangtong lists DIN 125A carbon steel zinc-plated flat washers from M3 to M36, and ASTM F436 / F436M hardened structural flat washers for A325 bolts in carbon steel heat-treated to 38–45 HRC, black oxide, hot-dip galvanised or plain, as round flat washers or square tapered washers. [3][4]
Editorial note: where a bolting specification calls for ASTM F436 washers, a plain washer to another standard does not meet it; name the standard and type on the order, and ask for hardness test results for hardened washers.
Give the supplier the standard and type, nominal size (bolt diameter), inner and outer diameter and thickness if non-standard, material and hardness, finish (zinc, hot-dip galvanised, black oxide, plain, stainless), the bolt grade it pairs with, quantity and packaging, and test or inspection certificates.
02
Check when bolting rules require washers
The Research Council on Structural Connections' 2020 Specification for Structural Joints Using High-Strength Bolts requires flat circular and beveled washers to meet ASTM F436 (except as given in its Table 6.1), of the same type as the bolt. Washers are not required in snug-tightened joints except where the outer face slopes more than 1:20 from a plane normal to the bolt axis (use an F436 beveled washer) or a slotted hole occurs in an outer ply (use an F436 washer or a "common plate washer" that completely covers the hole). In pretensioned and slip-critical joints, F436 washers are required under the nut when the calibrated wrench method is used, under both head and nut for Group 144 or 150 bolts in material with yield strength below 40 ksi, and as set out in Table 6.1 for oversized and slotted holes in the outer ply. [1]
The same specification lists nominal hole sizes, for example a 1/2 in bolt in a 9/16 in standard hole or 5/8 in oversized hole, and requires Engineer of Record approval for oversized holes, short slots not perpendicular to the applied load, and long slots in any direction. [1]
Editorial calculation: a 1:20 slope is about 2.9° from the plane normal to the bolt axis; steeper outer faces call for a beveled washer under this specification. [1]
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Compare what suppliers offer
Suppliers linked to this page list flat washers; each card links to the page reviewed.
The suppliers reviewed list flat washers with bolts, nuts and other fasteners; ask each for the standards and size ranges they make, material certificates, hardness results for hardened washers, coating thickness and packaging.
04
Trace the washer features
This is a functional reference built from the sources cited; it is not one maker's design.
Fill the specification fields with values for your joint
A flat washer quotation needs values for your joint. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
Field
What it means and published values
Ask the supplier for
Applicable Standard
E.g. DIN 125-A, ISO 7089, ASME B18.21.1, ASTM F436. [2]
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Published product pages show what a company offers, not tested performance. Confirm the legal seller, factory and scope for your order. How we source and review
· Page last updated 13 October 2026
Buyer questions
When are hardened washers required in structural bolting?
The RCSC 2020 specification requires ASTM F436 washers in cases such as the calibrated wrench method, Group 144/150 bolts in material under 40 ksi yield, and oversized or slotted holes in the outer ply. [1]
When is a beveled washer needed?
RCSC requires an F436 beveled washer where the outer face slopes more than 1:20 from the plane normal to the bolt axis. [1]
What sizes do DIN 125 flat washers come in?
Gangtong lists DIN 125A zinc-plated washers from M3 to M36. [3]
Sources and what still needs a direct check
Sources checked 2026-10-11. The RCSC specification is the consensus standard for US structural bolting; the suppliers describe their own products.
