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IS 6649:1980 is the Indian Standard (BIS) for high strength structural washers - specification. This standard specifies the material, dimensions, hardness, and other requirements for circular high-strength structural steel washers. These hardened washers are intended for use with high-strength structural bolts (e.g., Grade 8.8, 10.9) to ensure proper tensioning and distribute the clamping load.
Specifies requirements for plain washers for high strength structural bolting.
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Bridges and Bridge Engineering
! These hardened washers are essential to prevent 'cupping' and loss of preload when tightening high-strength bolts; do not substitute with mild steel washers.
! Hardness is the most critical property. It should be verified upon material receipt to ensure it is within the 35-45 HRC range.
! Ensure washers are placed under the element being turned (usually the nut) to distribute pressure and prevent galling.
Consolidated list per BIS. For the text of each amendment, refer to the BIS portal link above.
steelhigh strength steelfastenerswashers
International Equivalents
Similar International Standards
ASTM F436/F436M-19ASTM International, USA
HighCurrent
Standard Specification for Hardened Steel Washers
Specifies hardened steel washers for use with high-strength structural bolts.
EN 14399-6:2015CEN (European Committee for Standardization), Europe
HighCurrent
High-strength structural bolting assemblies for preloading - Part 6: Plain chamfered washers
Specifies plain chamfered washers as part of a high-strength structural bolting assembly.
ISO 7415:2020ISO (International Organization for Standardization), International
HighCurrent
Plain washers for high-strength structural bolting, hardened and tempered
Specifies requirements for hardened and tempered steel plain washers for high-strength bolting.
JIS B 1186:2022JSA (Japanese Standards Association), Japan
MediumCurrent
Sets of high strength hexagon bolt, hexagon nut and plain washers for friction grip joints
Covers the entire bolt, nut, and washer assembly, not just the washer in isolation.
Key Differences
≠The required hardness range in IS 6649 is 35 to 45 HRC, which is significantly higher than EN 14399-6 and ISO 7415 (300-370 HV, approx. 30-38 HRC) but similar to ASTM F436 Type 1 (38-45 HRC).
≠Dimensional specifications vary. For an M20 washer, IS 6649 specifies an outer diameter of 40 mm and thickness of 4 mm, whereas EN 14399-6/ISO 7415 specify an OD of 37 mm and thickness of 3 mm, making them not directly interchangeable.
≠Material chemistry requirements differ. For example, IS 6649 allows a maximum phosphorus content of 0.050%, while the more stringent EN 14399-6 limits it to 0.025%.
≠Marking requirements are distinct. IS 6649 requires the manufacturer's mark and standard number, while EN 14399-6 requires an 'H' mark and manufacturer ID, often linked to the specific bolting system (HR or HV).
Key Similarities
≈All standards cover washers specifically intended for use in high-strength structural bolting applications, designed to withstand high preload forces without cupping or yielding.
≈The manufacturing process across all standards requires the washers to be through-hardened and tempered to achieve the specified mechanical properties and ensure consistent performance.
≈The fundamental function is identical: to distribute the load from the bolt head or nut over a larger area on the connected steel members.
≈IS 6649, EN 14399-6, and ISO 7415 all mandate a chamfer on one edge of the outside diameter to ensure proper seating against the bolt head/nut fillet.
Parameter Comparison
Parameter
IS Value
International
Source
Hardness
35 to 45 HRC
300 to 370 HV (approx. 30-38 HRC)
EN 14399-6:2015
Hardness
35 to 45 HRC
38 to 45 HRC (for Type 1)
ASTM F436/F436M-19
Outer Diameter (for M20 bolt)
40.0 mm (nominal)
37.0 mm (nominal)
EN 14399-6:2015
Thickness (for M20 bolt)
4.0 mm (nominal)
3.0 mm (nominal)
EN 14399-6:2015
Thickness Range (for M20 bolt)
3.75 - 4.25 mm
3.1 - 4.9 mm
ASTM F436M-19
Material - Phosphorus (P), max %
0.050
0.025
EN 14399-6:2015
Material - Sulphur (S), max %
0.050
0.025
EN 14399-6:2015
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Required Hardness Range35 to 45 HRC
Nominal Thickness for M20 Washer4.0 mm
Inside Diameter for M20 Washer22.0 mm
Outside Diameter for M20 Washer42.0 mm
Applicable Bolt Property Classes8.8 and 10.9
Tables & Referenced Sections
Key Tables
Table 1 - Dimensions for High Strength Structural Washers