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Metric Steel Bolts - Grades and Property Classes

Metric steel bolts, screws and studs - proof and tensile strength.

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For metric bolts strength is according ISO 898 Mechanical properties of fasteners made of carbon steel and alloy steel described by "property classes" with designations 4.6, 4.8, 5.8, 8.8, 9.8, 10.9 and 12.9.

Property ClassHead MarkingSize Range
Minimum Proof Strength
(106 Pa)
Minimum Tensile Strength
(106 Pa)
4.6 Steel bolt - metric grade M5 - M36 225 400 Low or medium carbon steel
4.8 Steel bolt - metric grade M1.6 - M16 310 420 Low or medium carbon steel
5.8 Steel bolt - metric grade M5 - M24 380 520 Low or medium carbon steel
8.8 Steel bolt - metric grade M1.6 - M36 600 830 Medium carbon steel, Q & T
9.8 Steel bolt - metric grade M1.6 - M16 650 900 Medium carbon steel, Q & T
10.9 Steel bolt - metric grade M5 - M36 830 1040 Low carbon martensite steel, Q & T
12.9 Steel bolt - metric grade M1.6 - M36 970 1220 Alloy steel, Q & T
  • 1 Pa = 1 N/m2 = 1.4504x10-4 lb/in2 (psi)

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