Threaded steel fasteners — bolts, screws, studs, nuts and the washers under them — join steel structures, machines, flanges and equipment so that they can be assembled and taken apart. Their strength is set by a property class or grade, and a joint is only as good as the bolt, the nut and the tightening together.
A bolt is a headed rod threaded at one end and tightened with a nut; a screw is the same part threaded into a tapped hole or threaded nearly to the head; a stud bolt is threaded at both ends or along its whole length and used with two nuts, as on pipe flanges. Fasteners are cold or hot forged from wire rod and bar, the threads are rolled, and the higher grades are quenched and tempered to their strength.
Metric fasteners are graded by property class. On a bolt the class has two numbers: 8.8 means a nominal tensile strength of 800 N/mm² and a yield of 0.8 × that, 640 N/mm². Nuts carry a single number (8, 10, 12) and must be at least the class of the bolt. Inch fasteners use ASTM and SAE grades: A307 for ordinary carbon steel bolts, F3125 (which now contains A325 and A490) for structural bolts, and A193 B7 studs with A194 2H nuts for flanges in pressure piping.
Structural joints are either bearing joints, tightened snug, or preloaded (slip-resistant) joints, where high-strength bolts are tightened to a controlled tension. Preloaded joints in Europe use matched assemblies to EN 14399 — bolt, nut and washers made and tested together — and in the USA F3125 bolts with A563 nuts and F436 washers. Hot-dip galvanized fasteners need oversized nut threads and are always supplied as sets.
The GCC uses fasteners in very large numbers for structural steelwork, oil and gas plant, power and desalination projects. Most are imported, from China, India, Taiwan and Europe, and stocked by regional distributors; structural and pressure-piping fasteners are bought against project specifications that name the standard, the grade, the coating and the certificate. Metric fasteners dominate building work, while oil and gas piping uses inch stud bolts to ASTM A193 and A194 with ASME flanges.
A fastener is ordered by product standard, thread size and pitch, length, property class or grade, coating and quantity — for example 'M20 × 80 hexagon bolt ISO 4014, class 8.8, hot-dip galvanized, with ISO 4032 nut class 8'. See the metric thread and spanner size table.
Full dimensions: Metric coarse threads, hexagon bolt and nut sizes and spanner widths (ISO 4014 / 4017 / 4032)
| Region | Standard | What it covers |
|---|---|---|
| International | ISO 898-1 ISO |
Mechanical properties of bolts, screws and studs of carbon and alloy steel — property classes 4.6 to 12.9 |
| International | ISO 898-2 ISO |
Mechanical properties of nuts with specified property classes |
| International | ISO 4014 / ISO 4017 ISO |
Hexagon head bolts (partly threaded) and hexagon head screws (fully threaded), product grades A and B |
| International | ISO 4032 ISO |
Hexagon regular nuts |
| Germany | DIN 931 / DIN 933 / DIN 934 replaced by ISO 4014 / ISO 4017 / ISO 4032 |
Hexagon head bolts, screws and nuts — four sizes differ across flats from ISO (M10, M12, M14, M22) |
| Europe | EN 14399 CEN-CENELEC |
High-strength structural bolting assemblies for preloading — systems HR and HV |
| Europe | EN 15048 CEN-CENELEC |
Non-preloaded structural bolting assemblies |
| USA | ASTM F3125/F3125M ASTM |
High-strength structural bolts — grades A325, A490, F1852 and F2280 in one standard |
| USA | ASTM A325 replaced by ASTM F3125 |
Structural bolts, heat treated, 120/105 ksi minimum tensile strength |
| USA | ASTM A490 replaced by ASTM F3125 |
Structural bolts, alloy steel, heat treated, 150 ksi minimum tensile strength |
| USA | ASTM A193/A193M ASTM |
Alloy and stainless steel bolting for high-temperature or high-pressure service — grade B7 studs for flanges |
| USA | ASTM A194/A194M ASTM |
Nuts for bolts for high-pressure or high-temperature service — grades 2H, 4, 7 |
| USA | ASTM A307 ASTM |
Carbon steel bolts, studs and threaded rod, 60 ksi tensile strength |
| USA | ASTM F1554 ASTM |
Anchor bolts, steel, 36, 55 and 105 ksi yield strength |
| Japan | JIS B1180 / B1181 JSA |
Hexagon head bolts and screws; hexagon nuts |
| China | GB/T 5782 / 5783 / 6170 SAC |
Hexagon head bolts, fully threaded screws and nuts, aligned with ISO 4014, 4017 and 4032 |
| India | IS 1367 BIS |
Technical supply conditions for threaded steel fasteners |
Grade equivalents and the standards bodies: Steel grades & standards
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