ISO 898-1:2013, Table 3
Stamped 9.8. Medium carbon steel, quenched and tempered.
| Size range | Proof | Yield min | Tensile min | Core hardness |
|---|---|---|---|---|
| d = 1.6 mm through 16 mm | 650 MPa (94 ksi) | 720 MPa (104 ksi) | 900 MPa (131 ksi) | Rockwell C28 to C37 |
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 9.8 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 900 MPa; yield 0.8 of it, so 720 MPa.
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.
Medium carbon steel, quenched and tempered. Higher-strength general hardware, mostly in smaller diameters.
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 16 mm, ISO property class 9.8 requires a minimum tensile strength of 900 MPa (131 ksi), a minimum yield of 720 MPa (104 ksi) and a proof load of 650 MPa (94 ksi).
The class number 9.8 stamped on the head, with the manufacturer's identifier.
Medium carbon steel, quenched and tempered. Higher-strength general hardware, mostly in smaller diameters.
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:
ISO 898-1 core hardness in Rockwell C for classes 9.8, 10.9 and 12.9: 9.8: C28-C37, 10.9: C32-C39, 12.9: C39-C44 (iso898-sidex) against 9.8: C27-C36, 10.9: C33-C39, 12.9: C38-C44 (grades-wikipedia). The 2013 edition figures are printed, and all three ISO 898-1 extracts cross-checked here agree on them. The differing set matches earlier editions of the standard. A single Rockwell point either way does not change what the fastener is, but it can change whether an incoming inspection passes it, so the difference is recorded.
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