ISO/DIS 6157-4:2026(en)

ISO/TC 2

Secretariat: DIN

Date:2025-11-28

Fasteners — Surface discontinuities — Part 4: Washers

© ISO 2026

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zzContents

1 Scope 4

2 Normative references 4

3 Terms and definitions 4

4 Symbols 5

5 Discontinuities from raw materials and washer manufacturing process (including heat treatment, if any)

5.1 General 5

5.2 Burrs 5

5.2.1 General 5

5.2.2 Axial burr height, b_h 6

5.2.3 Shifted burr b_d1 and/or b_d2 8

5.3 Delamination, cracks, and seam and laps 8

5.4 Scratches, rolled-in scale and roll marks 9

5.5 Voids 10

5.6 Protrusions 11

5.7 Quench cracks 11

5.8 Scale 11

6 Discontinuities from coating process 12

6.1 General 12

6.2 Contact discontinuity 12

6.3 Local chipping 14

6.4 Uncoated areas 15

6.5 Packed washers 15

7 Inspection and evaluation procedure 15

Foreword

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This document was prepared by Technical Committee ISO/TC 2, Fasteners.

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Fasteners — Surface discontinuities — Part 4: Washers

This document specifies the limits for surface discontinuities of washers designed to be used in bolted joints in combination with bolts, screws, studs and nuts.

This document basically applies to the following washers manufactured from flat steel and stainless steel raw materials (such as strips), delivered in the uncoated or coated surface condition:

— plain washers (with or without knurls, ribs or chamfers),

— square washers,

— square hole washers,

— shaped plates,

— non-flat washers (e.g. conical, waved, curved, teethed, toothed washers, etc.),

— in steel with thickness 0,2 mm to 12 mm (see e.g. ISO 898-3),

— in stainless steel with thickness 0,2 mm to 6 mm (see e.g. ISO 3506-7).

This document (or part of it) is also applicable to other thickness or types of washers or similar parts (such as ribbed, knurled or serrated washers) by agreement between the purchaser and the supplier.

WARNING For the purpose of this document, surface discontinuities shown in Figures are sometimes exaggerated and/or chosen to make them visible and/or recognizable. Limits related to each discontinuities are defined in the following relevant Clauses.

Relevance of surface discontinuities in relation to the washer types is given in Annex A for guidance.

A multilingual list of terms used for washer surface discontinuities is also given in Annex B.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3269, Fasteners — Acceptance inspection

ISO 4042, Fasteners — Electroplated coating systems

ISO 10683, Fasteners — Non-electrolytically applied zinc flake coating systems

ISO 10684, Fasteners — Hot dip galvanized coatings

For the purposes of this document, the following terms and definitions apply, together with ISO 1891-2 for fastener coatings.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1

burr

excessive material at the cut edges of the washer resulting from punching process, laser cutting or machining

3.2

washer surface

area of the whole washer, including the vertical faces of the internal hole and external diameter

3.3

washer face

one or the other bearing side of the washer (i.e. excluding the internal hole and external diameter side)

For the purposes of this document, the following symbols apply:

Washers are produced from coils, sheets or plates (by cutting and punching process, or by laser cutting), or from bars (by machining). The washer manufacturer shall select the raw material in order to fulfil the requirements specified in this document.

In mass production, discontinuities resulting from raw material (see e.g. EN 10163), washer manufacturing process and heat treatment (if any) are occurring incidentally and can hardly be anticipated or controlled by monitoring a gradual drift.

The main types of discontinuities from raw materials and washer manufacturing process are shown in Figures 1, 2 and 4 to 13, and limits shall be as specified in this Clause 5.

NOTE Typical discontinuities shown in the following figures are selected to make them visible and/or recognizable; these figures are not intended to show limits or acceptability.

Discontinuities dealt with in this document shall be controlled on the washers in the as-received condition.

Burrs are resulting from the washer manufacturing process; they can appear at the whole circumference of the external diameter or hole diameter, or part of it.

The height of the burrs b_h is the distance between the washer face and a parallel plane located at the top of the burr.

Example of axial burr is shown in Figure 1 and example of shifted burr is shown in Figure 2.

Figure 1 — Example of axial burr

Figure 2 — Example of shifted burr

All washers of all types shall be deburred before coating (if any).

Burrs shall be controlled on the washers in the as-received condition (uncoated or coated).

Dimensional measurements for clearance hole d₁, outside diameter d₂ and thickness t of a washer shall be performed in areas where burrs, if any, do not influence the dimensional determination. For shifted burr, see 5.2.3.

The part of the burrs protruding above the washer faces (in the direction of the washer axis, see Figures 1 and 2) shall be controlled.

b_h shall be measured by mean of any suitable testing device (e.g. a dial gauge, optical or laser measurement, etc.), see Figure 3.

Key

1 sensor first positioned on the washer face (reference point)

2 sensor then positioned at the top of the burr

Figure 3 — Example of measurement of burr height with a dial gauge

The washer to be controlled should be held in position to avoid any unexpected move during measurement. In case of a circular burr, the highest point shall be measured. In case of several burrs on the same washer, the highest burr shall be measured.

When measured with a dial gauge, the sensor shall be placed perpendicularly to the material thickness on the washer face near to the burr to be measured (see key 1 in Figure 3), in order to minimize the possible flatness influence. The display of the sensor shall be set to zero. Then, the sensor shall be placed on the top of the burr (see key 2 in Figure 3) and moved slightly to either side until the highest point is observed. The corresponding burr height b_h shall be recorded.

Burr height shall be in accordance with the limits specified in Table 1 for the relevant product grade specified in the product standard or technical specification. For washers with no specified product grade (e.g. non-flat washers, washers per drawing, etc.), the applicable column shall be agreed between the purchaser and the manufacturer at the time of the order.

For specific applications, “no sharp burr” can also be agreed between the purchaser and the manufacturer at the time of the order. In this case, a protrusion at the edge of 2 % of the thickness can be agreed as maximum burr height.

Table 1 — Limits for burr height

Dimensions in millimetres

In case of dispute and if nothing has been specified before the order, column (2) shall apply for free washers and column (1) for captive washers.

In case of dispute about burr height determination, measuring by mean of a dial gauge with a flat cylindrical contact sensor of 1 to 3 mm in diameter and contact force of 1,8 N maximum shall be used as the reference test method.

The part of the burrs, bd1, protruding at the clearance hole d₁ (about perpendicular to the washer axis, see Figure 2) shall not result in a value less than d_1,min, with d_1,min as specified in the product standard or technical specification.

The diameter d_1,min shall be evaluated with any suitable means. In case of dispute, the control with a GO-gauge is the reference test method.

The part of the burrs, b_d2, protruding at the outside diameter d₂ (about perpendicular to the washer axis, see Figure 2) shall not result in d_2,max to be exceeded, with d₂,_max as specified in the product standard or technical specification.

Delamination, cracks, and seam and laps for washers are internal longitudinal splits or lamination cracks in the raw material that create layers, generally parallel to the surface of the coil, sheet or plate, see Figure 4, 5 and 6.

Figure 4 — Appearance of delamination

Figure 5 — Appearance of cracks

Figure 6 — Appearance of seam and lap

Limits: Delamination, cracks, and seam and laps of any depth, any length, or in any location are not allowed.

Scratchs, rolled-in scale and roll marks are longitudinal tool marks on the washer face coming from the raw material or from the washer manufacturing process, see Figure 7, 8 and 9. They result from the lamination process of the coils, sheets or plates (e.g. from rollers or scale) or from the feeding device during washers manufacturing process.

Figure 7 — Appearance of scratches

Figure 8 — Appearance of rolled-in scale

Figure 9 — Appearance of roll mark

Limits for product grades A and F: Localized scratches, rolled-in scale and roll marks shall not be cause of rejection, unless otherwise specified by the purchaser at the time of the order. If such discontinuities are going through the whole washer face, its depth shall be less than 10 % of the effective washer thickness t_eff but with a maximum depth of 0,25 mm.

Limits for product grade C: Localized scratches, rolled-in scale and roll marks shall not be cause of rejection, unless otherwise specified by the purchaser at the time of the order. If such discontinuities are going through the whole washer face, its depth shall be less than 20 % of the effective washer thickness t_eff but with a maximum depth of 0,5 mm.

Avoid is a shallow pocket or hollow at the washer face, resulting from indented mark during the washer manufacturing process or from local lack of metal in the raw material. With regards to raw material, rust can lead to a local lack of metal; with regards to the washer manufacturing process, indents may happen on the washer face from a tool mark, a broken tool, free chips or chip clump, or from another washer. Voids are not flattened during the washer manufacturing process. See Figure 10.

Figure 10 — Appearance of voids

Limits for product grades A and F: The depth of the void shall be less than 5 % of the effective washer thickness teff but with a maximum depth of 0,25 mm. Additionally, the combined area of all voids on one face shall not exceed 5 % of its surface for washers with nominal diameter d₁ ≤ 24 mm, and 10 % above. In case of dispute, the method to evaluate the impacted area shall be agreed between the purchaser and the supplier.

Limits for product grade C: The depth of the void shall be less than 10 % of the effective washer thickness t_eff but with a maximum depth of 0,5 mm. Additionally, the combined area of all voids on one face shall not exceed 20 % of its surface. In case of dispute the method to evaluate the impacted area shall be agreed between the purchaser and the supplier.

A protrusion is a localized metal excess resulting in a thick solid burr in approximately the same direction than the washer axis, which cannot be removed by deburring. It comes from the washer manufacturing process and usually results from a local breakage of the cutting edge of the tool. See Figure 11.

Figure 11 — Example of protrusion

Limits: Protrusions exiting the washer face shall not exceed the limits specified for burrs in accordance with 5.2.

For heat treated washers, a quench crack is a clean crystalline fracture passing through or across the grain boundaries or possibly following inclusions, caused by overstressing the metal during the quenching process. Quench cracks usually follow an irregular and erratic course at the surface of the washer. See Figure 12.

Figure 12 — Appearance of quench crack

Limits: Quench cracks of any depth, any length or in any location are not allowed.

For uncoated washers, scale is the presence of black oxide spots on the washer surface resulting from quenching and tempering process. See Figure 13.

Figure 13 — Example of scale

Limits: Unless specifically agreed before the order, scale shall not be cause of rejection.

When steel washers are coated for corrosion protection purpose, differences in the local coating thickness cannot be avoided and will vary depending on the washer size and thickness, the type of coating and the coating process; these may cause differences in the local corrosion resistance.

Electroplated coatings for fasteners are specified in ISO 4042. Non-electrolytically applied zinc flake coatings for fasteners are specified in ISO 10683. Hot dip galvanized coatings for fasteners are specified in ISO 10684. Other types of coating (e.g. mechanically applied coatings according to ISO 12683, etc.) are by agreement between the purchaser and the supplier. For terms and definitions related to fastener coatings, see ISO 1891-2.

Temporary protections (typically less than 5 µm in thickness) or coatings mainly intended for decorative purpose are not dealt with in this Clause 6: a particular agreement shall be reached between the purchaser and the supplier before the order.

The main types of discontinuities from coating process are shown in Figures 14 to 19, and limits shall be as specified in this Clause 6.

NOTE Typical discontinuities shown in the following figures are selected to make them visible and/or recognizable; these figures are not intended to show limits or acceptability.

Discontinuities dealt with in this document shall be controlled on the washers in the as-received condition.

Contact discontinuity results from bulk process (for the coating itself or for finishes such as top coat or sealer) where washers and similar flat fasteners tend to stick together (the thinner and lighter the parts, the more likely they are to stick together and this phenomenon cannot be avoided unless specific rack process). See Figures 14, 15 and 16.

Figure 14 — Examples of contact discontinuities

Limits:

a) For electroplating systems in accordance with ISO 4042 and for non-electrolytically applied zinc flake coating systems in accordance with ISO 10683, lower local coating thickness shall not be cause of rejection. In case of dispute, the corrosion resistance specified in the relevant standard shall be decisive for acceptance.

b) For hot dip galvanized coating in accordance with ISO 10684, local coating thickness and coating average thickness as specified in ISO 10684 shall be decisive for acceptance.

c) For other types of coating, an agreement shall be reached between the purchaser and the supplier at the time of the order.

d) For steel fasteners with captive washer(s) coated after assembly, the following additional specifications shall apply:

— for electroplated coating systems in accordance with ISO 4042 and for non-electrolytically applied zinc flake coating systems in accordance with ISO 10683: there may be areas with lower coating thickness between washer and the mating fastener, and/or between the washers, due to the geometry of these fasteners and related coating process; this may result in a locally reduced corrosion resistance and should not be cause for rejection considering that these areas are normally not exposed to environmental corrosion in service;

— other types of coating and plating: when shot blasting is used for the preparation of the surface before coating, retention of particles may impair the free rotation of the washer (see ISO 10644); this risk increases with increasing ratio t/d₁ for the washers; suitable measures should be considered to mitigate it (e.g. blasting media type and size selection, appropriate shaking with vibrational devices, etc.); the free rotation of the washer on its mating fastener shall be decisive for acceptance.

— when the washer external diameter d₂ is less or approximately equal to the bearing surface of the bolt/screw or nut, washer(s) tend(s) to stick to the bearing face of its mating fastener, thus impairing the free rotation of the washer(s) (see ISO 10644); the free rotation of the washer on its mating fastener shall be decisive for acceptance.

Figure 15 — Example of contact discontinuities resulting in local excess of coating

Limits: Local excess of coating shall not be cause of rejection, providing that it does not impair the specified functional properties.

Key

1 local red rust spot

Figure 16 — Examples of contact discontinuities resulting in lack of coating

Limits: Washers delivered by the manufacturer shall not show zones of red rust. For coatings providing cathodic protection and for which self-healing occurs, small lack of coating shall not be cause of rejection. In case of dispute, the method to evaluate the red spots area shall be agreed between the purchaser and the supplier, and the impacted area shall not exceed 3 % of the washer surface.

Local chipping usually results from bulk process where abrasion and/or impact can occur especially at washer edges and for soft coatings. See Figure 17.

Figure 17 — Examples of local chipping by abrasion or impact

Limits: Washers delivered by the manufacturer shall not show zones of red rust. For coatings providing cathodic protection and for which self-healing occurs, local chipping shall not be cause of rejection. In case of dispute, the method to evaluate the chipping area shall be agreed between the purchaser and the supplier, and the impacted area shall not exceed 3 % of the washer surface.

Uncoated areas result from the coating layer peeled-off from the basis metal, usually caused by the combination of raw material, heat treatment and/or poor cleaning or descaling. See Figure 18.

Figure 18 — Example of uncoated areas

Limits: The coated washer shall be free from uncoated areas.

Packed washers result from washers sticking together during bulk coating process, typically for hot dip galvanized coatings and zinc flake coatings (during curing). This is more susceptible to happen for washers with small size (e.g. light parts and/or thin parts). See Figure 19.

Figure 19 — Examples of packed washers

Limits for washers with product grades A and F, or when specifically requested: a maximum of 3% of packed washers is acceptable within the manufacturing lot.

Limits for other washers: a maximum of 5 % of packed washers is acceptable within the manufacturing lot.

When particular specifications are needed, sorting may be required by agreement between the purchaser and the supplier before the order.

Unless otherwise agreed, washers in accordance with this document shall be capable of conforming to all applicable requirements specified in Clause 5 for discontinuities from raw materials and washer manufacturing process, and in Clause 6 for coated washers.

This document does not mandate which controls or tests the manufacturer shall perform on each manufacturing lot. It is the responsibility of the manufacturer to apply suitable methods of their choice, such as in-process control or final inspection, to ensure that the manufactured lot does indeed conform to the specified requirements.

In case of dispute and when no prior agreement exists, ISO 3269 applies but for the purpose of washer surface discontinuities, the requirements for inspection categories specified in Table 2 shall apply and do supersede the generic inspection category 1 of ISO 3269.

Table 2 — Inspection categories for washer surface discontinuities

If sorting is required for one or more characteristic(s), an agreement shall be reached between the purchaser and the supplier before the order (see ISO 16426 for more information).

1. 
   (informative)
   
   Relevance of surface discontinuities in relation to the types of washers

This document specifies several surface discontinuities for washers. However, not all surface discontinuities are relevant for all types of washers primarily due to their shapes and/or for functional reasons.

This Annex provides guidance about the applicability to flat washers, elastic washers, and teethed or toothed washers, see Tables A.1 to A.3 respectively.

Table A.1 — Flat washers

Table A.2 — Elastic washers

Table A.3 — Teethed or toothed washers

1. 
   (informative)
   
   Multilingual list of terms for washer surface discontinuities

In addition to the terms used in the three official ISO languages (English, French and Russian), this International Standard gives the equivalent terms in Chinese, German, Italian, Japanese, Spanish and Swedish; these have been included at the request of ISO Technical Committee ISO/TC 2 and are published under the responsibility of the member bodies for China (SAC), Germany (DIN), Italy (UNI), Japan (JISC), Spain (AENOR) and Sweden (SIS). However, only the terms given in the official languages can be considered as ISO terms.

Bibliography

ISO 898‑3, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 3: Flat washers with specified property classes

ISO 1891‑2, Fasteners — Terminology — Part 2: Vocabulary and definitions for coating

ISO 3506‑7, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 7: Flat washers with specified grades and property classes

ISO 10644, Screw and washer assemblies made of steel with plain washers — Washer hardness classes 200 HV and 300 HV

ISO 12683, Mechanically deposited coatings of zinc — Specification and test methods

ISO 16426, Fasteners — Quality assurance system