Ungalvanized Steel Hexagon Head Bolts

Give the thread and length as in the IMPA description (for example M12 × 50 mm). An M designation without a pitch means coarse pitch, the default from ISO 261 / ISO 262 — 1.75 mm for M12, 2 mm for M16, 2.5 mm for M20; a fine-pitch bolt must be ordered with its pitch stated (M12 × 1.25 and so on).^[1]

State the property class where strength matters. In ISO 898-1 classes for carbon and alloy steel bolts, the first number is the tensile strength in MPa divided by 100 and the second the ratio of yield to tensile strength: 4.6 is a mild-steel bolt of 400 MPa tensile and 240 MPa yield, 8.8 a high-strength bolt of 800 MPa and 640 MPa. A bolt with no marking is treated as low strength, so do not fit one where a marked 8.8 bolt came out.^[2]

Check the spanner size if it matters on the job: at some sizes ISO and DIN hex heads differ — 16 mm against 17 mm across flats for M10, 18 against 19 mm for M12, 21 against 22 mm for M14.^[1]

Metric hexagon bolts and screws are specified in, for example, ISO 4014 and ISO 4017, and their mechanical properties in ISO 898-1, which covers bolts, screws and studs of carbon and alloy steel; corrosion-resistant steel fasteners are covered by ISO 3506-1.^[2][3]