Mechanical requirements by diameter
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 head marking
Marked A325 on the head, with the manufacturer's identifier.
The specification stamped in full. Type 3 weathering steel adds an underline.
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.
Material and where it is used
Medium carbon steel, quenched and tempered (Type 1). Structural steel connections in buildings and bridges.
A325 was withdrawn as a standalone specification and its requirements now sit in ASTM F3125 as Grade A325. Bolts are still marked and ordered as A325.
One older chart cross-checked here splits the range three ways - 85 ksi for 1/2 to 3/4, 78 ksi for 7/8 and 1, 74 ksi above - against the two-band split every other source gives. The two-band figures are printed.
Frequently asked questions
How strong is a ASTM A325 bolt?
Over 1/2 in through 1 in, ASTM A325 requires a minimum tensile strength of 120 ksi (827 MPa), a minimum yield of 92 ksi (634 MPa) and a proof load of 85 ksi (586 MPa). The requirement changes in the larger sizes - 2 diameter bands are published in all.
What does a ASTM A325 head marking look like?
Marked A325 on the head, with the manufacturer's identifier.
What is a ASTM A325 bolt made of?
Medium carbon steel, quenched and tempered (Type 1). Structural steel connections in buildings and bridges.
Does ASTM A325 get weaker in larger sizes?
The requirement changes with diameter. 1/2 in through 1 in: 85 ksi (586 MPa) proof; Over 1 in through 1-1/2 in: 74 ksi (510 MPa) proof. Quoting one figure across the whole range gets part of it wrong.
What this section covers
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.
Where these figures come from
Dimensions are as defined by ASTM A325 (withdrawn and rolled into ASTM F3125). 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 4 independent published sources:
ASTM A325 proof stress bands: 85 ksi to 1 in, 74 ksi above (grades-wikipedia) against 85 ksi to 1 in, 74 ksi above (grades-aft) against 85 ksi to 3/4 in, 78 ksi for 7/8 and 1 in, 74 ksi above (grades-fmw). The two-band split is printed. The three-band version appears in one older chart and matches a superseded edition of A325; it is recorded rather than deleted because a reader holding that chart deserves to know why the numbers differ.