ASTM F436 / F436M Hardened Steel Washers | Specifications

Standard Overview

What Are ASTM F436 & F436M?

The North American standard for hardened steel washers used in structural steel connections, slip-critical joints, and bridge construction.

ASTM F436 covers hardened steel washers for use with high-strength structural bolts. These washers are through-hardened to prevent embedding under the high preload of ASTM A325, A490, and F1852 bolts (now consolidated under ASTM F3125). The standard is available in two series:

Inch Series

ASTM F436

For use with inch-series structural bolts (A325, A490, F1852, F2280). Sizes from 1/2" to 1-1/2" nominal bolt diameter.

Dimensions: ASME B18.22.1 | Thread: UNC / UNF

Metric Series

ASTM F436M

For use with metric structural bolts (A325M, A490M). Sizes from M12 to M36 nominal bolt diameter.

Dimensions: Metric equivalent sizing | Thread: Metric coarse

                        Critical Requirement: ASTM F436 washers are not interchangeable with standard commercial washers or ISO 7089 soft washers. They are specifically hardened to 38–45 HRC to withstand the proof loads of high-strength structural bolts. Using a soft washer under an A490 bolt will cause embedding, preload loss, and potential joint failure.
                    

Technical Specifications

Types, Materials & Hardness

Types 1 & 3

Type 1 — Carbon Steel: Plain carbon steel, quenched and tempered. Used with plain or galvanized structural bolts in general construction. Most common type.
Type 3 — Weathering Steel: High-strength low-alloy steel with atmospheric corrosion resistance. Used with weathering steel (A588 / Cor-Ten) structures to prevent galvanic corrosion between dissimilar metals. Matches the rust patina of weathering steel.

Mechanical Properties

Property	Type 1 (Carbon Steel)	Type 3 (Weathering Steel)
Hardness	38 – 45 HRC	38 – 45 HRC
Hardness (HBW)	321 – 444	321 – 444
Carburization	Not permitted	Not permitted
Decarburization	Not permitted	Not permitted
Surface Finish	Plain or HDG	Plain (self-colour)

Washers must be through-hardened, not case-hardened. Carburization or decarburization is prohibited because it creates a soft core or brittle surface that compromises load-bearing capacity under structural preload.

Chemical Composition

Element	Type 1	Type 3
Carbon (C)	0.15 – 0.55%	0.15 – 0.55%
Phosphorus (P)	≤ 0.040%	0.06 – 0.15%
Sulfur (S)	≤ 0.050%	≤ 0.050%
Copper (Cu)	—	≥ 0.20%
Chromium (Cr)	—	0.30 – 1.25%
Nickel (Ni)	—	≤ 0.65%
Vanadium (V)	—	0.02 – 0.10%

Type 3 weathering steel contains copper, chromium, and phosphorus to develop a protective oxide patina. This prevents the staining and galvanic corrosion that would occur if Type 1 washers were used on weathering steel structures.

Dimension Tables

ASTM F436 & F436M Dimensions

Dimensions in inches (F436) and millimetres (F436M). All values nominal with ASME B18.22.1 tolerances.

ASTM F436 — Inch Series

Bolt Size	ID (min)	ID (max)	OD (min)	OD (max)	Thickness (min)	Thickness (max)
1/2"	0.531	0.562	1.062	1.125	0.177	0.192
5/8"	0.688	0.719	1.312	1.375	0.177	0.192
3/4"	0.812	0.844	1.469	1.531	0.177	0.192
7/8"	0.938	0.969	1.750	1.812	0.177	0.192
1"	1.062	1.094	2.000	2.062	0.177	0.192
1-1/8"	1.188	1.250	2.250	2.312	0.177	0.192
1-1/4"	1.312	1.375	2.500	2.562	0.177	0.192
1-3/8"	1.438	1.500	2.750	2.812	0.177	0.192
1-1/2"	1.562	1.625	3.000	3.062	0.177	0.192

ASTM F436M — Metric Series

Bolt Size	ID (min)	ID (max)	OD (min)	OD (max)	Thickness (min)	Thickness (max)
M12	13.0	13.5	24.0	25.0	4.0	4.6
M16	17.0	17.5	30.0	31.0	4.0	4.6
M20	21.0	22.0	37.0	38.0	4.0	4.6
M22	23.0	24.0	39.0	40.0	4.0	4.6
M24	25.0	26.0	44.0	45.0	4.0	4.6
M27	28.0	29.0	50.0	51.0	4.0	4.6
M30	31.0	32.0	56.0	57.0	4.0	4.6
M36	37.0	38.0	66.0	67.0	4.0	4.6

                    Tapered Washers for Beams: For sloped surfaces (typically 1:6 or 1:20 on tapered flanges), specify ASTM F436 beveled washers. These are square or rectangular washers machined with a taper to provide full flat bearing on angled structural steel surfaces. Standard flat F436 washers must never be used on beveled surfaces.
                

Application Guidance

Where & How to Use F436 Washers

Structural Steel Connections

Mandatory under ASTM F3125 bolting assemblies. F436 washers prevent embedding of the bolt head or nut into the steel plate under proof load, maintaining consistent preload in slip-critical and bearing-type joints.

Bridges & Infrastructure

Type 3 weathering steel washers are specified for bridges and highway structures built with A588 / Cor-Ten steel. The washer develops the same protective rust patina as the structure, eliminating galvanic mismatch.

Turn-of-Nut Method

During structural bolting, the F436 washer is placed under the element being turned (nut or bolt head). The hardened surface allows controlled rotation without galling or embedding during the turn-of-nut tightening procedure.

Oversize & Slotted Holes

When bolts pass through oversize or slotted holes in structural steel, F436 washers must be used under both the bolt head and nut to bridge the gap and provide full bearing surface. Standard plate washers may be required for very large holes.

Coastal UAE Projects

For structural steel in UAE coastal environments, specify hot-dip galvanized (HDG) Type 1 F436 washers paired with HDG F3125 bolts. For weathering steel structures, specify Type 3 plain finish. Never mix plain and HDG washers on the same connection.

Complete RFQ Format

"ASTM F436 Type 1 hardened steel washer, 3/4", plain finish, 38–45 HRC, with ASTM F3125 Grade A325 bolt assembly."

Related Standards

Complementary Structural Bolting Standards

Standard	Description	Relationship to F436
ASTM F3125	High-strength structural bolts (A325, A490, F1852, F2280)	F436 washers are mandatory companion hardware
ASTM A194	Heavy hex nuts for high-strength bolting	2H / 2HM nuts paired with F3125 bolts
ASTM A563	Carbon & alloy steel nuts	DH nuts for A325 bolts; DH3 for weathering
ASME B18.22.1	Plain washers — dimensions	Dimensional basis for F436 inch series
ASTM F959	Compressible-washer-type direct tension indicators	Squirter washers for tension control bolting
ASTM A325	Structural bolts, steel, heat treated (legacy)	Now F3125 Grade A325; requires F436 washer
ASTM A490	Structural bolts, alloy steel, heat treated (legacy)	Now F3125 Grade A490; requires F436 washer
RCSC Specification	Specification for Structural Joints Using High-Strength Bolts	Governs installation, inspection, and washer use
AISC 360	Specification for Structural Steel Buildings	References F436 for structural connections
ISO 7089	Plain washers, normal series, Grade A	Metric general-purpose; NOT for structural bolting

FAQ

Frequently Asked Questions

What is the difference between ASTM F436 and F436M?

F436 is the inch-series standard for use with UNC/UNF structural bolts (A325, A490). F436M is the metric-series standard for use with metric coarse structural bolts (A325M, A490M). The hardness requirements (38–45 HRC) and material grades (Types 1 and 3) are identical. The only difference is dimensional sizing.

Can I use a commercial washer instead of ASTM F436?

Absolutely not. Commercial washers (including ISO 7089 soft washers) are not hardened and will embed under the proof load of A325 or A490 bolts. This causes preload loss, joint slip, and potential structural failure. F436 washers are specifically through-hardened to 38–45 HRC to resist embedding. Always use F436 with F3125 structural bolts.

When should I use Type 3 instead of Type 1?

Use Type 3 (weathering steel) when bolting weathering steel structures such as A588 / Cor-Ten bridges and facades. Type 3 develops a protective oxide patina that matches the base metal. Using Type 1 on weathering steel creates a galvanic cell and causes premature rust staining. Type 1 is standard for painted or galvanized carbon steel structures.

Do I need one washer or two per bolt?

Per RCSC Specification: Use one F436 washer under the element being turned (nut or bolt head) during tightening. For oversize or slotted holes, use two washers — one under the bolt head and one under the nut — to bridge the hole and provide full bearing. For very large holes, plate washers may be required in addition to F436.

Can F436 washers be hot-dip galvanized?

Yes. Type 1 F436 washers can be hot-dip galvanized per ASTM A153. However, galvanizing must not reduce the hardness below 38 HRC. Always pair HDG F436 washers with HDG F3125 bolts and A563 DH hot-dip galvanized nuts. Type 3 washers are typically supplied plain (self-colour) and are not galvanized.

What is the difference between F436 and F959 (DTI) washers?

F436 is a standard hardened flat washer for load distribution. F959 is a Direct Tension Indicator (DTI) — a compressible washer with protrusions that flatten under preload. The gap between the DTI and bolt is measured with a feeler gauge to verify that the bolt has been tightened to the required tension. F959 is used for tension-control installation; F436 is used for turn-of-nut or calibrated wrench methods.

Need ASTM F436 / F436M Washers in UAE?

We stock ASTM F436 and F436M hardened steel washers in Type 1 (carbon steel) and Type 3 (weathering steel), plain and hot-dip galvanized. Full certification, hardness test reports, and same-day dispatch from RAK FREEZONE across UAE & GCC.

Request a Quote