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Resources/Cross-references/Bolt property classes

Cross-references

Bolt grades and property classes compared: SAE Grade 5 / 8, ASTM A325 / A490, ISO 8.8 / 10.9 / 12.9

Metric bolts in the UK, EU, India and Japan all use the ISO 898-1 property classes (4.6, 8.8, 10.9, 12.9), while US inch bolts use SAE J429 grades and ASTM specifications. SAE Grade 5 and ASTM A325 (120 ksi) are close to class 8.8, and SAE Grade 8 and ASTM A490 (150 ksi) are close to class 10.9.

Cross-reference

Equivalent grades by region

LevelUSASAE J429; ASTM A307, ASTM F3125 (A325, A490), ASTM A193UKBS EN ISO 898-1 (bolts), BS EN ISO 898-2 (nuts)EUEN ISO 898-1 (bolts), EN ISO 898-2 (nuts)IndeIS 1367 (Part 3) bolts, IS 1367 (Part 6) nutsJapanJIS B 1051 (bolts), JIS B 1052-2 (nuts)
Low strength, ~400–420 MPa tensileASTM A307 Grade A (tensile ≥60 ksi / 414 MPa); SAE J429 Grade 2 over 3/4 in (tensile 60 ksi)4.6 (Rm ≥400 MPa, ReL ≥240 MPa); 4.8 (Rm ≥420 MPa)4.6 / 4.84.6 / 4.84.6 / 4.8
Low-medium strength, ~510–520 MPa tensileGrade 2 is the closest inch match to 5.8 by tensile strength; its yield (57 ksi / 393 MPa) is lower.SAE J429 Grade 2, 1/4–3/4 in (tensile 74 ksi / 510 MPa, proof 55 ksi)5.8 (Rm ≥520 MPa, yield ≥420 MPa)5.85.85.8
Medium-carbon, quenched and tempered, ~800–830 MPa tensileGrade 5 above 1 in drops to 105 ksi tensile. Older A325 editions also dropped to 105 ksi above 1 in; F3125 Grade A325 is 120 ksi for all diameters.SAE J429 Grade 5 (1/4–1 in: tensile 120 ksi / 827 MPa, proof 85 ksi); ASTM F3125 Grade A325 (tensile 120 ksi, all sizes)8.8 (Rm ≥800 MPa ≤M16, ≥830 MPa >M16; Rp0.2 ≥640 / 660 MPa)8.88.8 (structural HSFG: 8.8S to IS 3757)8.8
Alloy steel, quenched and tempered, ~1000–1040 MPa tensileGrade 8 (1034 MPa) is marginally below the 10.9 minimum (1040 MPa) and has a lower proof stress, so the two are closest rather than identical.SAE J429 Grade 8 (tensile 150 ksi / 1034 MPa, proof 120 ksi); ASTM F3125 Grade A490 (tensile 150–173 ksi)10.9 (Rm ≥1040 MPa, Rp0.2 ≥940 MPa)10.910.9 (structural HSFG: 10.9S to IS 3757)10.9; structural friction-grip sets F10T (JIS B 1186)
Highest strength, ~1220 MPa tensileClass 12.9 is used mainly for socket head cap screws. Inch socket screws are made to their own ASTM specifications rather than an SAE J429 grade.—12.9 (Rm ≥1220 MPa, Rp0.2 ≥1100 MPa)12.912.912.9
Alloy studs for high-temperature, high-pressure serviceB7 is usually specified under its ASTM name worldwide. Its strength sits between 8.8 and 10.9, and it falls with diameter (115 ksi over 2-1/2 to 4 in).ASTM A193 B7 (≤2-1/2 in: tensile 125 ksi / 862 MPa, yield 105 ksi / 724 MPa)————
Matching nutsA nut class matches the first number of the bolt class: an 8.8 bolt takes a class 8 nut, a 10.9 bolt a class 10 nut.SAE J995 Grade 5 / 8; ASTM A563; ASTM A194 2H (for A193 B7)Classes 5, 8, 10, 12 (BS EN ISO 898-2)Classes 5, 8, 10, 12 (EN ISO 898-2)Classes 5, 8, 10, 12 (IS 1367 Part 6); 8S / 10S for HSFG (IS 6623)Classes 5, 8, 10, 12 (JIS B 1052-2)

Read before comparing

  • How to read a property class such as 8.8: the first number × 100 is the nominal tensile strength in MPa (800); the second number × 10 is the yield-to-tensile ratio in percent (80 %), so the nominal yield is 800 × 0.8 = 640 MPa. Class 10.9 is 1000 MPa nominal tensile and 900 MPa nominal yield.
  • Specified minimums differ slightly from the nominal values: 8.8 is 800 MPa up to M16 and 830 MPa above; 10.9 is 1040 MPa and 12.9 is 1220 MPa.
  • SAE J429 grades are identified by radial lines on the head: none for Grade 2, three for Grade 5, six for Grade 8. ISO classes are stamped as numbers (8.8, 10.9).
  • IS 1367 (Part 3):2017 is adopted identically from ISO 898-1:2013, so Indian property classes are the ISO classes. JIS B 1051:2014 corresponds to ISO 898-1:2013.
  • ASTM F3125 replaced A325, A490, F1852 and F2280 in 2015. Bolts are still marked and ordered as Grade A325 and Grade A490 under F3125.
  • Inch and metric fasteners are not interchangeable even at similar strength: thread forms, pitches and nut classes differ. Compare strength at the actual size, as SAE Grade 2 and Grade 5 drop in strength above 3/4 in and 1 in respectively.

Questions et réponses

Common questions

Is Grade 8 the same as 10.9?

Close but not identical. SAE Grade 8 has a 150 ksi (1034 MPa) minimum tensile strength and 120 ksi proof stress; class 10.9 has 1040 MPa tensile and 830 MPa proof stress. They are the usual like-for-like swap, but inch and metric threads are not interchangeable.

Is Grade 5 equivalent to 8.8?

Yes, approximately. SAE Grade 5 up to 1 in has a 120 ksi (827 MPa) minimum tensile strength; class 8.8 has 800 MPa up to M16 and 830 MPa above. Both are medium-carbon, quenched and tempered steel.

What does 8.8 mean on a bolt?

The first 8 means a nominal tensile strength of 800 MPa; the second 8 means the yield is 80 % of that, 640 MPa. The same rule reads 10.9 as 1000 MPa tensile and 900 MPa yield.

What is the metric equivalent of an A325 bolt?

ASTM F3125 Grade A325 (120 ksi minimum tensile) is closest to property class 8.8. For structural friction-grip joints the metric counterparts are 8.8 bolt sets to EN 14399 or IS 3757; A490 is closest to 10.9.

Is 12.9 stronger than Grade 8?

Yes. Class 12.9 has a 1220 MPa (about 177 ksi) minimum tensile strength, against 150 ksi (1034 MPa) for SAE Grade 8. It is also less ductile and more sensitive to hydrogen embrittlement, which limits plating and galvanizing.

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Keep reading

ISO metric (M)ISO metric threads are 60° V-threads designated by M, the major diameter in millimetres and, for fine pitches, the pitch in millimetres (M12 is coarse, M12×1.25 is fine).UNC / UNFUNC (Unified coarse) and UNF (Unified fine) are 60° inch threads designated by diameter and threads per inch, such as 1/2-13 UNC or 1/2-20 UNF.4140 / 42CrMo4AISI 4140 is a medium-carbon chromium-molybdenum alloy steel, normally used hardened and tempered for shafts, gears and high-strength bolts.1045 / C451045 is a medium-carbon steel with about 0.45 % carbon, supplied hot rolled, normalized or quenched and tempered for shafts, pins, gears and forgings.Galvanizing standardsHot-dip galvanizing is specified by ASTM A123 (fabrications), A153 (hardware) and A767 (rebar) in the USA, EN ISO 1461 in the UK and EU, IS 4759 in India and JIS H 8641 in Japan.Zinc electroplatingZinc electroplating deposits a thin, even layer of zinc on steel from an electrolyte bath, usually 5–25 µm thick, and is normally sealed with a chromate passivate.

References

Sources

  1. T&R Fastenings: mechanical properties of steel bolts to ISO 898-1
  2. Fastenal: mechanical properties of inch fasteners (SAE J429, ASTM A307, A325, A490, A193 B7)
  3. Portland Bolt: strength requirements by grade
  4. Portland Bolt: changes to A325 since its incorporation into F3125
  5. ASTM F3125/F3125M-25 (consolidated structural bolting specification)
  6. Bureau of Indian Standards: IS 1367 (Part 3):2017, identical with ISO 898-1:2013
  7. Bureau of Indian Standards: IS 3757 high-strength structural bolts (8.8 and 10.9)
  8. Miki Pulley: mechanical properties of steel bolts and screws (JIS B 1051 excerpt)
  9. JIS B 1186:2013 sets of high-strength hexagon bolt, nut and washers for friction grip joints

Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.