ISO 898-1:2013, Table 3
Stamped 12.9. Alloy steel, quenched and tempered.
| Size range | Proof | Yield min | Tensile min | Core hardness |
|---|---|---|---|---|
| d = 1.6 mm through 100 mm | 970 MPa (141 ksi) | 1100 MPa (160 ksi) | 1220 MPa (177 ksi) | Rockwell C39 to C44 |
Inch grades are published in ksi and metric classes in MPa. The other column on every row is a conversion at 1 ksi = 6.894757 MPa, rounded to the nearest whole unit - it is arithmetic on the published figure, not a second published figure.
The class number 12.9 stamped on the head, with the manufacturer's identifier.
The two numbers are the strength, not a serial number. The first times 100 is the nominal tensile strength in MPa; the two multiplied together times 10 is the nominal yield. Class 8.8 is 800 MPa tensile and 640 MPa yield, and you can read that straight off the head. Nominal tensile 1200 MPa; yield 0.9 of it, so 1080 MPa nominal, 1100 MPa minimum.
Count the radial lines and add two. That rule identifies exactly two grades - SAE Grade 5 with three lines and SAE Grade 8 with six - and it fails everywhere else. Grades 1, 2 and 4 carry no marking at all, so an unmarked head is not evidence of Grade 2; it is evidence of nothing, and unmarked hardware that meets no standard looks exactly the same. ASTM grades are stamped with the specification (A325, A490, BC, BD, 307A) rather than lines, and metric classes are stamped with the class number. Four marking systems share one bin.
Alloy steel, quenched and tempered. The highest common class - precision machinery and socket head cap screws.
Metric classes are marked with a number, not a line count. There is no metric equivalent of the radial-line system.
Over d = 1.6 mm through 100 mm, ISO property class 12.9 requires a minimum tensile strength of 1220 MPa (177 ksi), a minimum yield of 1100 MPa (160 ksi) and a proof load of 970 MPa (141 ksi).
The class number 12.9 stamped on the head, with the manufacturer's identifier.
Alloy steel, quenched and tempered. The highest common class - precision machinery and socket head cap screws.
Twenty-two grades and classes: the SAE J429 inch grades, five ASTM specifications and the ISO 898-1 property classes. It is not every grade in circulation. Stainless classes (ISO 3506 A2 and A4, ASTM F593), the ASTM A193 and A320 high and low temperature grades, ASTM F1554 anchor rod grades and SAE grades 3, 5.1 and 8.1 are not carried here.
Dimensions are as defined by ISO 898-1:2013, Table 3. This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 3 independent published sources:
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