Property class (fasteners)
Property class: the two-digit strength designation for metric fasteners (4.6, 8.8, 10.9). First digit x 100 = tensile strength MPa. AS 4291.1:2015.
Ask Chalkline about this →Property class is the two-digit designation stamped on metric bolts, screws, and studs that identifies their mechanical strength, per AS 4291.1:2015. The first digit multiplied by 100 gives the minimum nominal tensile strength in megapascals (MPa). The product of both digits multiplied by 10 gives the minimum yield strength (or proof stress) in MPa.
For example, a property class 4.6 fastener has a minimum tensile strength of 400 MPa and a minimum yield strength of 240 MPa. A class 8.8 fastener has a minimum tensile strength of 800 MPa and minimum yield strength of 640 MPa. The marking appears on the bolt head or screw head.
In residential construction, class 4.6 covers general-purpose bolts and coach screws; class 8.8 applies to high-strength structural bolt assemblies under AS/NZS 1252.1:2016. The classes look the same on-site, so checking the head marking on delivery is the only reliable way to confirm grade. Never substitute class 4.6 where 8.8 is specified.
Also known as: bolt grade, fastener grade, strength grade.
Category: Fastener specifications.
Standard: AS 4291.1:2015 (verified 2026-05-10, Standards Australia Store).
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Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.