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Steel Bolts Strength Designation System

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Strength Grade Designation System for Steel Nuts

Strength Grade Designation System for Steel Bolts and Screws:

The strength grade designation system consists of two figures. The first figure is one tenth of the minimum tensile strength in kgf/mm², and the second figure is one tenth of the ratio between the minimum yield stress (or stress at permanent set limit, R_0.2) and the minimum tensile strength, expressed as a percentage.

For example with the strength designation grade 8.8, the first number "8" represents 1⁄10 the minimum tensile strength of 80 kgf/mm² and the second number "8" represents 1⁄10 the ratio

the numerical values of stress and strength being obtained from the table given below.

Strength Grade Designation System of Steel Bolts and Screws

Strength Grade Designation	4.6	4.8	5.6	5.8	6.6	6.8	8.8	10.9	12.9	14.9
Tensile Strength (Rm), Min.	40	40	50	50	60	60	80	100	120	140
Yield Stress (Re), Min.	24	32	30	40	36	48	…	…	…	…
Stress at Permanent Set Limit (R0.2), Min.	…	…	…	…	…	…	64	90	108	126
All stress and strength values are in kgf/mm2 units.