Bolt grade and property class chart.

The two numbers on a metric bolt head are its property class. In 8.8 the first number × 100 gives the nominal tensile strength (800 MPa) and the second × 10 gives the yield ratio (80%). The tables give the ISO 898-1 minimums, stainless classes and the nearest inch grades.

Reviewed 11 Nov 2026 · Based on ISO 898-1:2013 Mechanical properties of fasteners made of carbon steel and alloy steel; ISO 3506-1:2020 Corrosion-resistant stainless steel fasteners; SAE J429; ASTM A193/A193M · Report an error

Download the printable chart (PDF)

Questions on this?

Quenched and tempered; the common structural class. The first number × 100 is the nominal tensile strength in MPa; the second × 10 is the yield ratio in percent.

800MPa minimum tensile, 640 MPa yield, 580 MPa proof
M6 proof load
11.7 kN
M8 proof load
21.2 kN
M10 proof load
33.6 kN
M12 proof load
48.9 kN
M16 proof load
90.9 kN
M20 proof load
142.0 kN
M24 proof load
204.5 kN

Proof load = proof stress × stress area (ISO 898-1). Classes marked d ≤ 16 apply up to M16 only.

Quote this

Carbon and alloy steel, ISO 898-1 (MPa)
ClassNominal tensileMin. tensile RmMin. yield ReL / Rp0.2Proof stress SpNotes
4.6400400240225Low-carbon steel, general purpose
4.8400420340310Low-carbon steel, cold-headed
5.6500500300280Medium-carbon steel
5.8500520420380Low or medium-carbon steel
6.8600600480440Low or medium-carbon steel
8.8 (d ≤ 16)800800640580Quenched and tempered; the common structural class
8.8 (d > 16)800830660600Quenched and tempered
9.8 (d ≤ 16)900900720650Quenched and tempered; up to M16 only
10.910001040940830Quenched and tempered alloy or boron steel
12.9120012201100970Quenched and tempered alloy steel; hydrogen-embrittlement risk if electroplated
Source: ISO 898-1:2013. Class 9.8 applies up to M16 only; 8.8 values change above M16.
Stainless steel bolts, ISO 3506-1 (MPa)
ClassMin. tensile RmMin. 0.2% proof Rp0.2
A2-50 / A4-50500210
A2-70 / A4-70700450
A2-80 / A4-80800600
Source: ISO 3506-1:2020. A2 = 304-type steel, A4 = 316-type (molybdenum) for chlorides and marine use.
Inch grades (ksi)
GradeSizesMin. tensileMin. yieldNearest metric class
SAE J429 Grade 21/4 to 3/4 in74574.6 to 5.6
SAE J429 Grade 51/4 to 1 in120928.8
SAE J429 Grade 5over 1 to 1-1/2 in105818.8
SAE J429 Grade 81/4 to 1-1/2 in15013010.9
ASTM A193 B7up to 2-1/2 in125105close to 8.8 / 10.9; specify A193 B7 by name
Source: SAE J429; ASTM A193/A193M. Equivalents are approximate: specify the grade the drawing calls for.

Reference values, not a design.

Values are the nominal figures of the cited standards, or calculated from them where marked. The governing standard and your drawing always take precedence.

All tools

Questions buyers ask.

What is the difference between 8.8 and 10.9 bolts?

Class 10.9 has a minimum tensile strength of 1,040 MPa against 800 to 830 MPa for 8.8, and a proof stress of 830 MPa against 580 to 600 MPa (ISO 898-1). 10.9 carries more load at the same size; 8.8 is the common structural class.

Is grade 8.8 the same as SAE Grade 5?

They are close but not identical. SAE J429 Grade 5 requires 120 ksi (about 827 MPa) tensile up to 1 inch; ISO 898-1 class 8.8 requires 800 MPa up to M16 and 830 MPa above. Specify the standard your drawing uses.

What is the difference between A2 and A4 stainless bolts?

A2 is 304-type austenitic stainless steel; A4 is 316-type with molybdenum, which resists chlorides better, so it is preferred for marine, coastal and chemical environments. Both come in classes 50, 70 and 80 (ISO 3506-1).

Send your drawing. We reply within one business day.

Specification, quantity and destination. PDF, DWG, DXF and STEP welcome.

Request a quote