Hexagon head bolts and hex cap screws from M3 to M150 and ¼″ to 6″, forged and thread-rolled in stainless steel, alloy steel, duplex, Inconel, Monel, Hastelloy and titanium, every lot shipped with EN 10204 3.1 / 3.2 certificates and PMI.
A hex bolt is an externally threaded fastener with a six-sided head, driven by a spanner or socket and tightened against a nut or into a tapped hole. It is the most widely specified fastener in industry because the hexagon gives the largest practical bearing face and driving surface for its size.
Exotic Alloy manufactures hexagon head bolts and hex cap screws in Mumbai, India, to ISO 4014 / ISO 4017, DIN 931 / DIN 933, ASME B18.2.1, BS 3692, IS 1364 and JIS B 1180. Standard carbon and alloy steel bolts are cold forged; stainless, duplex, nickel alloy and titanium bolts are hot forged or machined from certified bar, then thread rolled for fatigue strength. We export to the UAE, Saudi Arabia, Qatar, Oman, Europe and the Americas.
ASTM A193 B7, B8, B8M and stainless A2-70 / A4-80 hex bolts ship from stock. Inconel 625 / 718, Monel 400 / K-500, Hastelloy C-276, Incoloy 825, duplex 2205, super duplex 2507 and titanium grade 5 hex bolts are forged to order in 7 to 15 business days, in any length and thread pitch to your drawing.
The envelope we manufacture and stock. Anything outside it is made to drawing.
The same hexagon head is produced to several dimensional standards. The differences are the thread length, the width across flats and the tolerance grade, and they matter when a bolt has to fit an existing spanner, hole or nut.
Plain shank under the head and a thread length set by the 2d + 6 / 12 / 25 mm rule. The unthreaded shank carries shear across the joint and locates the parts. Product grade A up to M24 and L ≤ 10d or 150 mm; grade B above.
Threaded right up to the head so the nut or tapped hole can engage at any grip length. The usual choice for short lengths, tapped holes and where the clamped thickness varies. Same head and thread as ISO 4014.
ASME separates the hex cap screw (washer face under the head, closer head tolerances, chamfered point, made to length) from the hex bolt (plain underhead, wider tolerances). UNC and UNF threads to ASME B1.1 class 2A. Thread length 2D + ¼″ up to 6″ long.
Width across flats 1½D + ⅛″ instead of 1½D, giving a larger bearing face for flanges and structural steel. Used with heavy hex nuts (ASME B18.2.2 / A194 2H, 8M) on ASME B16.5 flanges and in slip-critical structural joints.
Fine threads (M8x1, M10x1.25, M12x1.25 / 1.5, M16x1.5, M20x1.5 and so on) give a larger stress area, finer adjustment and better resistance to loosening under vibration. Standard in automotive, hydraulics and machine tools.
Hot forged with wider dimensional tolerances and 8g thread, in class 4.6 / 4.8 / 5.6. The economical structural and general-engineering bolt, usually hot-dip galvanised for outdoor steelwork, towers and foundations.
The ISO standards replaced the DIN head sizes on four diameters. Thread, head height and length are identical, so the bolts are interchangeable in the joint, but the spanner size is not. State the standard you need, especially for maintenance stock.
| Size | M10 | M12 | M14 | M22 |
|---|---|---|---|---|
| DIN 931 / 933 across flats | 17 mm | 19 mm | 22 mm | 32 mm |
| ISO 4014 / 4017 across flats | 16 mm | 18 mm | 21 mm | 34 mm |
| Type | ISO | DIN | ASME / SAE | BS | IS (India) | JIS | UNI |
|---|---|---|---|---|---|---|---|
| Hex bolt, partial thread, grade A/B | ISO 4014 | DIN 931 | ASME B18.2.1 hex cap screw | BS 3692 | IS 1364 Pt 1 | JIS B 1180 | UNI 5737 |
| Hex screw, full thread, grade A/B | ISO 4017 | DIN 933 | ASME B18.2.1 hex cap screw | BS 3692 | IS 1364 Pt 2 | JIS B 1180 | UNI 5739 |
| Hex bolt / screw, grade C | ISO 4016 / 4018 | DIN 601 | ASME B18.2.1 hex bolt | BS 4190 | IS 1363 Pt 1 / 2 | JIS B 1180 | — |
| Hex bolt / screw, fine pitch | ISO 8765 / 8676 | DIN 960 / 961 | ASME B18.2.1 (UNF) | BS 3692 | — | JIS B 1180 | — |
| Heavy hex bolt / screw | — | — | ASME B18.2.1 heavy hex | — | — | — | — |
| Heavy hex structural bolt | — | DIN 6914 | ASME B18.2.6 (F3125) | BS EN 14399-4 | IS 3757 | JIS B 1186 | — |
| Imperial precision hex bolt (UNC / UNF) | — | — | ASME B18.2.1 | BS 1768 | — | — | — |
Nominal dimensions. Width across corners e is shown as the geometric value 1.155 × s; the standards list slightly smaller minimum values that allow for the corner chamfer. Tolerances are to product grade A or B of the standard quoted.
| Size | Pitch P mm | s (ISO) A/F mm | s (DIN 931/933) A/F mm | e ≈ 1.155 s A/C mm | k mm | b, L ≤ 125 mm | b, 125 < L ≤ 200 mm | b, L > 200 mm | As mm² |
|---|---|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.5 | 5.5 | 6.4 | 2 | 12 | 18 | 31 | 5.03 |
| M4 | 0.7 | 7 | 7 | 8.1 | 2.8 | 14 | 20 | 33 | 8.78 |
| M5 | 0.8 | 8 | 8 | 9.2 | 3.5 | 16 | 22 | 35 | 14.2 |
| M6 | 1 | 10 | 10 | 11.5 | 4 | 18 | 24 | 37 | 20.1 |
| M8 | 1.25 | 13 | 13 | 15.0 | 5.3 | 22 | 28 | 41 | 36.6 |
| M10 | 1.5 | 16 | 17 | 18.5 | 6.4 | 26 | 32 | 45 | 58 |
| M12 | 1.75 | 18 | 19 | 20.8 | 7.5 | 30 | 36 | 49 | 84.3 |
| M14 | 2 | 21 | 22 | 24.2 | 8.8 | 34 | 40 | 53 | 115 |
| M16 | 2 | 24 | 24 | 27.7 | 10 | 38 | 44 | 57 | 157 |
| M18 | 2.5 | 27 | 27 | 31.2 | 11.5 | 42 | 48 | 61 | 192 |
| M20 | 2.5 | 30 | 30 | 34.6 | 12.5 | 46 | 52 | 65 | 245 |
| M22 | 2.5 | 34 | 32 | 39.3 | 14 | 50 | 56 | 69 | 303 |
| M24 | 3 | 36 | 36 | 41.6 | 15 | 54 | 60 | 73 | 353 |
| M27 | 3 | 41 | 41 | 47.3 | 17 | 60 | 66 | 79 | 459 |
| M30 | 3.5 | 46 | 46 | 53.1 | 18.7 | 66 | 72 | 85 | 561 |
| M33 | 3.5 | 50 | 50 | 57.7 | 21 | 72 | 78 | 91 | 694 |
| M36 | 4 | 55 | 55 | 63.5 | 22.5 | 78 | 84 | 97 | 817 |
| M39 | 4 | 60 | 60 | 69.3 | 25 | 84 | 90 | 103 | 976 |
| M42 | 4.5 | 65 | 65 | 75.1 | 26 | 90 | 96 | 109 | 1121 |
| M45 | 4.5 | 70 | 70 | 80.8 | 28 | 96 | 102 | 115 | 1306 |
| M48 | 5 | 75 | 75 | 86.6 | 30 | 102 | 108 | 121 | 1473 |
| M52 | 5 | 80 | 80 | 92.4 | 33 | 110 | 116 | 129 | 1758 |
| M56 | 5.5 | 85 | 85 | 98.1 | 35 | 118 | 124 | 137 | 2030 |
| M60 | 5.5 | 90 | 90 | 103.9 | 38 | 126 | 132 | 145 | 2362 |
| M64 | 6 | 95 | 95 | 109.7 | 40 | 134 | 140 | 153 | 2676 |
Scroll inside the table for M18 to M64. Highlighted across-flats values are where DIN 931 / 933 differ from ISO 4014 / 4017. Thread length b applies to partially threaded bolts; fully threaded screws (ISO 4017 / DIN 933) are threaded to within a few pitches of the head. As is the ISO 898-1 nominal stress area used for proof and tensile loads.
| Size | Threads/in UNC | A/F hex in | Head height H in | A/F heavy hex in | Thread length, L ≤ 6″ in | Thread length, L > 6″ in |
|---|---|---|---|---|---|---|
| 1/4″ | 20 | 7/16 | 5/32 | — | 0.75 | 1.00 |
| 5/16″ | 18 | 1/2 | 13/64 | — | 0.88 | 1.12 |
| 3/8″ | 16 | 9/16 | 15/64 | — | 1.00 | 1.25 |
| 7/16″ | 14 | 5/8 | 9/32 | — | 1.12 | 1.38 |
| 1/2″ | 13 | 3/4 | 5/16 | 7/8 | 1.25 | 1.50 |
| 9/16″ | 12 | 13/16 | 23/64 | — | 1.38 | 1.62 |
| 5/8″ | 11 | 15/16 | 25/64 | 1-1/16 | 1.50 | 1.75 |
| 3/4″ | 10 | 1-1/8 | 15/32 | 1-1/4 | 1.75 | 2.00 |
| 7/8″ | 9 | 1-5/16 | 35/64 | 1-7/16 | 2.00 | 2.25 |
| 1″ | 8 | 1-1/2 | 39/64 | 1-5/8 | 2.25 | 2.50 |
| 1-1/8″ | 7 | 1-11/16 | 11/16 | 1-13/16 | 2.50 | 2.75 |
| 1-1/4″ | 7 | 1-7/8 | 25/32 | 2 | 2.75 | 3.00 |
| 1-3/8″ | 6 | 2-1/16 | 27/32 | 2-3/16 | 3.00 | 3.25 |
| 1-1/2″ | 6 | 2-1/4 | 15/16 | 2-3/8 | 3.25 | 3.50 |
| 1-3/4″ | 5 | 2-5/8 | 1-3/32 | 2-3/4 | 3.75 | 4.00 |
| 2″ | 4-1/2 | 3 | 1-7/32 | 3-1/8 | 4.25 | 4.50 |
Basic (nominal) dimensions for hex cap screws. Standard hex across flats is 1½D (with the usual exceptions at ¼″, ⅜″, ½″, ⅝″, ⅞″ and 1″); heavy hex is 1½D + ⅛″. UNF (fine) threads are supplied to the same head dimensions.
A hex bolt is specified by two things: the dimensional standard (above) and the strength grade. The grade is marked on the head. The tables below give the guaranteed minimums for the grades we manufacture.
| Property class | Tensile Rm nom MPa | Tensile Rm min MPa | Yield ReL / Rp0.2 min MPa | Proof stress Sp MPa | Elongation A min % | Hardness |
|---|---|---|---|---|---|---|
| 4.6 | 400 | 400 | 240 | 225 | 22 | 120–220 HV |
| 4.8 | 420 | 420 | 340 | 310 | 14 | 130–220 HV |
| 5.6 | 500 | 500 | 300 | 280 | 20 | 155–220 HV |
| 5.8 | 520 | 520 | 420 | 380 | 10 | 160–220 HV |
| 6.8 | 600 | 600 | 480 | 440 | 8 | 190–250 HV |
| 8.8 (d ≤ M16) | 800 | 800 | 640 | 580 | 12 | 250–320 HV / 22–32 HRC |
| 8.8 (d > M16) | 800 | 830 | 660 | 600 | 12 | 255–335 HV / 23–34 HRC |
| 9.8 | 900 | 900 | 720 | 650 | 10 | 290–360 HV / 28–37 HRC |
| 10.9 | 1000 | 1040 | 940 | 830 | 9 | 320–380 HV / 32–39 HRC |
| 12.9 | 1200 | 1220 | 1100 | 970 | 8 | 385–435 HV / 39–44 HRC |
Classes 4.6 to 6.8 are low or medium carbon steel, not heat treated. Class 8.8 and above are quenched and tempered; 8.8 and 9.8 from medium carbon steel with or without boron, 10.9 from medium carbon alloy steel, 12.9 from alloy steel. Below M16 the 8.8 limits are 800 / 640 MPa; above M16 they rise to 830 / 660 MPa.
| Size | As mm² | Proof load 8.8 kN | Proof load 10.9 kN | Proof load 12.9 kN | Min. breaking load 8.8 kN | Min. breaking load 10.9 kN | Min. breaking load 12.9 kN |
|---|---|---|---|---|---|---|---|
| M6 | 20.1 | 11.7 | 16.7 | 19.5 | 16.1 | 20.9 | 24.5 |
| M8 | 36.6 | 21.2 | 30.4 | 35.5 | 29.3 | 38.1 | 44.7 |
| M10 | 58 | 33.6 | 48.1 | 56.3 | 46.4 | 60.3 | 70.8 |
| M12 | 84.3 | 48.9 | 70.0 | 81.8 | 67.4 | 87.7 | 102.8 |
| M14 | 115 | 66.7 | 95.5 | 111.5 | 92.0 | 119.6 | 140.3 |
| M16 | 157 | 91.1 | 130.3 | 152.3 | 125.6 | 163.3 | 191.5 |
| M18 | 192 | 115.2 | 159.4 | 186.2 | 159.4 | 199.7 | 234.2 |
| M20 | 245 | 147.0 | 203.3 | 237.7 | 203.3 | 254.8 | 298.9 |
| M22 | 303 | 181.8 | 251.5 | 293.9 | 251.5 | 315.1 | 369.7 |
| M24 | 353 | 211.8 | 293.0 | 342.4 | 293.0 | 367.1 | 430.7 |
| M27 | 459 | 275.4 | 381.0 | 445.2 | 381.0 | 477.4 | 560.0 |
| M30 | 561 | 336.6 | 465.6 | 544.2 | 465.6 | 583.4 | 684.4 |
| M33 | 694 | 416.4 | 576.0 | 673.2 | 576.0 | 721.8 | 846.7 |
| M36 | 817 | 490.2 | 678.1 | 792.5 | 678.1 | 849.7 | 996.7 |
Proof load = As × proof stress Sp; minimum breaking load = As × Rm,min. A bolt loaded to its proof load must show no permanent set.
| Steel group | Property class | Tensile Rm min MPa | Yield Rp0.2 min MPa | Elongation A min | Typical grades |
|---|---|---|---|---|---|
| A2 (austenitic Cr-Ni) | 50 / 70 / 80 | 500 / 700 / 800 | 210 / 450 / 600 | 0.6d / 0.4d / 0.3d | AISI 304, 304L, 321, 347 |
| A4 (austenitic Cr-Ni-Mo) | 50 / 70 / 80 | 500 / 700 / 800 | 210 / 450 / 600 | 0.6d / 0.4d / 0.3d | AISI 316, 316L, 316Ti, 317L |
| A5 (austenitic Cr-Ni-Mo, stabilised) | 50 / 70 / 80 | 500 / 700 / 800 | 210 / 450 / 600 | 0.6d / 0.4d / 0.3d | 316Ti |
| C1 (martensitic) | 50 / 70 / 110 | 500 / 700 / 1100 | 250 / 410 / 820 | 0.2d / 0.2d / 0.2d | AISI 410 |
| F1 (ferritic) | 45 / 60 | 450 / 600 | 250 / 410 | 0.2d / 0.2d | AISI 430 |
Austenitic classes 70 and 80 are produced by cold working, so the strength that can be reached falls with increasing diameter: the hex bolt product standards ISO 4014 / 4017 list A2-70 and A4-70 up to M24 and A2-50 / A4-50 above M24 to M39, with class 80 and larger diameters in class 70 supplied by agreement. Elongation is measured as a fraction of the nominal diameter d. Austenitic stainless bolts are non-magnetic in the annealed state and become slightly magnetic after cold working.
| Grade | Material | Diameter | Tensile min ksi (MPa) | Yield min ksi (MPa) | Elong. min % | RA min % | Hardness max | Impact test |
|---|---|---|---|---|---|---|---|---|
| A193 B7 | AISI 4140-type Cr-Mo, Q&T | ≤ 2½″ | 125 (862) | 105 (724) | 16 | 50 | 35 HRC | — |
| A193 B7M | Cr-Mo, Q&T, controlled hardness | ≤ 4″ | 100 (689) | 80 (552) | 18 | 50 | 235 HBW / 22 HRC | — |
| A193 B16 | Cr-Mo-V, Q&T | ≤ 2½″ | 125 (862) | 105 (724) | 18 | 50 | 35 HRC | — |
| A193 B8 Cl.1 | AISI 304, solution annealed | all | 75 (517) | 30 (207) | 30 | 50 | 223 HBW / 96 HRB | — |
| A193 B8M Cl.1 | AISI 316, solution annealed | all | 75 (517) | 30 (207) | 30 | 50 | 223 HBW / 96 HRB | — |
| A193 B8 Cl.2 | AISI 304, strain hardened | ≤ ¾″ | 125 (862) | 100 (689) | 12 | 35 | 321 HBW / 35 HRC | — |
| A193 B8 Cl.2 | AISI 304, strain hardened | > ¾ to 1″ | 115 (793) | 80 (552) | 15 | 35 | 321 HBW / 35 HRC | — |
| A193 B8M Cl.2 | AISI 316, strain hardened | ≤ ¾″ | 110 (758) | 95 (655) | 15 | 45 | 321 HBW / 35 HRC | — |
| A193 B8M Cl.2 | AISI 316, strain hardened | > ¾ to 1″ | 100 (689) | 80 (552) | 20 | 45 | 321 HBW / 35 HRC | — |
| A320 L7 | Cr-Mo (4140-type), Q&T | ≤ 2½″ | 125 (862) | 105 (724) | 16 | 50 | 35 HRC | 27 J (20 ft·lbf) at −101 °C |
| A320 L7M | Cr-Mo, Q&T, controlled hardness | ≤ 2½″ | 100 (689) | 80 (552) | 18 | 50 | 235 HBW | 27 J (20 ft·lbf) at −73 °C |
| A320 L43 | AISI 4340-type Ni-Cr-Mo, Q&T | ≤ 4″ | 125 (862) | 105 (724) | 16 | 50 | 35 HRC | 27 J (20 ft·lbf) at −101 °C |
| A320 B8 / B8M Cl.1 | AISI 304 / 316, solution annealed | all | 75 (517) | 30 (207) | 30 | 50 | 223 HBW | 27 J at −196 °C |
A193 covers bolting for high-temperature and high-pressure service; A320 covers low-temperature service and adds a Charpy impact requirement. B7M and L7M are the controlled-hardness versions used for sour service to NACE MR0175 / ISO 15156. Mate with A194 2H, 2HM, 8, 8M or 7 nuts.
| Grade / spec | Head marking | Diameter | Proof load ksi | Yield min ksi | Tensile min ksi | Material |
|---|---|---|---|---|---|---|
| ASTM A307 Gr. A | 307A | ¼ to 4″ | — | — | 60 | Low-carbon steel |
| SAE J429 Gr. 2 | none | ¼ to ¾″ | 55 | 57 | 74 | Low / medium carbon |
| SAE J429 Gr. 2 | none | > ¾ to 1½″ | 33 | 36 | 60 | Low / medium carbon |
| SAE J429 Gr. 5 | 3 radial lines | ¼ to 1″ | 85 | 92 | 120 | Medium carbon, Q&T |
| SAE J429 Gr. 5 | 3 radial lines | > 1 to 1½″ | 74 | 81 | 105 | Medium carbon, Q&T |
| SAE J429 Gr. 8 | 6 radial lines | ¼ to 1½″ | 120 | 130 | 150 | Medium carbon alloy, Q&T |
| ASTM F3125 Gr. A325 | A325 (Type 3: A325) | ½ to 1½″ | 85 | — | 120 | Medium carbon or alloy, Q&T (heavy hex structural); F3125 removed the old 105 ksi tier above 1″ |
| ASTM F3125 Gr. A490 | A490 (Type 3: A490) | ½ to 1½″ | 120 | — | 150–173 | Alloy steel, Q&T (heavy hex structural) |
Every grade below links to its full datasheet on this site: composition, mechanical and physical properties, equivalents and corrosion data. We forge hex bolts from certified bar in all of them.
Low carbon for 4.6 / 4.8, medium carbon (1035 to 1045 type) quenched and tempered for 8.8 and Grade 5. Usually zinc plated or hot-dip galvanised.
Chromium-molybdenum 4140 / 4142 for B7, L7, 10.9 and 12.9; nickel-chromium-molybdenum 4340 for L43 and large diameter 10.9; B16 (Cr-Mo-V) for steam service to 540 °C.
450 MPa yield, twice that of 316, with resistance to chloride stress corrosion cracking. Offshore topsides, FPSOs, heat exchangers and flue gas desulphurisation.
PREN above 40, 550 MPa yield, for seawater, desalination, subsea manifolds and sour wells. Available NACE MR0175 compliant.
825 for sulphuric / phosphoric acid and sour gas; 800 series for furnace bolting; Nimonic 80A for gas turbines.
Silicon bronze for marine and architectural bolting, naval brass for fresh and salt water, nickel aluminium bronze for propellers, pumps and non-sparking duty.
| Alloy | UNS | Condition supplied | Tensile min MPa | Yield 0.2 % min MPa | Elongation % | Why it is chosen for hex bolts |
|---|---|---|---|---|---|---|
| Inconel 625 | N06625 | Solution annealed (Grade 1) | 827 | 414 | 30 | Seawater, sour gas, cryogenic to 980 °C oxidation; subsea flange bolting |
| Inconel 718 | N07718 | Solution treated + aged (AMS 5662) | 1240 | 1035 | 12 | Highest strength to 650 °C; turbine and wellhead bolting |
| Monel 400 | N04400 | Hot-finished annealed | 517 | 207 | 35 | Seawater, hydrofluoric acid, no chloride SCC; marine and valve bolting |
| Monel K-500 | N05500 | Age hardened (AMS 4676) | 960 | 690 | 18 | Monel 400 corrosion resistance with three times the yield; pump shafts, subsea |
| Hastelloy C-276 | N10276 | Solution annealed (ASTM B574) | 690 | 283 | 40 | Wet chlorine, hot acids, mixed oxidising / reducing media; chemical reactors |
| Incoloy 825 | N08825 | Annealed (ASTM B425) | 586 | 241 | 30 | Sulphuric and phosphoric acid, sour gas (NACE MR0175); pickling plant |
| Duplex 2205 | S32205 | Solution annealed | 655 | 450 | 25 | Twice the yield of 316 with chloride SCC resistance; offshore topsides |
| Super Duplex 2507 | S32750 | Solution annealed | 750 | 550 | 15 | PREN > 40; seawater and desalination bolting |
| Titanium Grade 5 | R56400 | Annealed (ASTM B348) | 895 | 828 | 10 | Half the weight of steel, immune to seawater; aerospace and chemical |
| A-286 | S66286 | Solution treated + aged | — | — | — | Iron-base superalloy for 650 °C bolting; on request with certified values |
Values are the minimums published on the linked datasheets for the supply condition shown; they are the material properties, not an ISO 898-1 property class. Where a project specification calls for ASTM F468 bolt properties or a specific heat treatment, we certify to that document.
Two routes, chosen by material and quantity. Both end with rolled threads, heat treatment where the grade requires it and 100 % inspection.
Bar and wire rod received against mill certificates; XRF / OES positive material identification on every heat of stainless and nickel alloy.
Carbon and alloy steel up to about M24 is cold forged on multi-station headers. Larger sizes, stainless, duplex, nickel alloys and titanium are induction-heated and hot forged, which refines grain and keeps the grain flow continuous into the head.
Hexagon trimmed, underhead fillet formed, point chamfered. Short runs and large diameters are CNC machined from hexagon or round bar to the same drawing.
Threads are rolled between flat dies or planetary dies rather than cut, work hardening the flanks and leaving the grain flow unbroken at the root. Rolled after heat treatment on request for maximum fatigue life (A193 B7, 10.9, 12.9).
Quench and temper for 8.8 and above, B7, L7 and 4140 grades; solution annealing for austenitic and duplex stainless; precipitation hardening for Monel K-500, Inconel 718 and A-286 in controlled-atmosphere furnaces with charted cycles.
Pickling and passivation for stainless; phosphate, zinc, hot-dip galvanising, zinc flake, PTFE or cadmium as specified; baking after plating for class 10.9 and above.
Thread gauging, head and length checks, hardness on every lot, tensile / proof load, wedge tensile and Charpy where the specification requires, then EN 10204 3.1 or 3.2 certification and marked, labelled packing.
Rolling displaces metal into the thread form instead of removing it. The flanks and root are cold worked and left in compression, the grain follows the profile, and the surface is smoother than a cut thread. The result is a markedly higher fatigue strength at the thread root, which is where hex bolts fail in service, together with better thread accuracy and no cutting marks to start corrosion.
Cut threads remain the right choice for very large diameters, extra-long bolts, special pitches and small quantities in hard-to-form alloys; we state the method on the certificate.
Carbon and alloy steel hex bolts need a coating; stainless and nickel alloy bolts need passivation and, in most assemblies, an anti-seize. See also our coated fasteners page.
| Finish | Specification | Typical thickness | Corrosion protection | Notes for hex bolts |
|---|---|---|---|---|
| Plain / black phosphate & oil | ISO 9717 / DIN EN 12476 | 2 – 5 μm | Indoor, oiled storage only | Standard supply for A193 B7, L7, 8.8 to 12.9; good base for PTFE; friction μ about 0.14 oiled |
| Zinc electroplate, trivalent passivated | ASTM B633 (SC1 – SC4) / ISO 4042 | 5 – 25 μm | 72 to 200 h neutral salt spray depending on thickness and passivation | Clear, yellow or black; thread tolerance kept at 6g; bake within 4 h of plating for class 10.9 and above (hydrogen embrittlement relief) |
| Hot-dip galvanised (HDG) | ISO 10684 / ASTM F2329 / IS 1367 Pt 13 | ≥ 40 μm local, ≥ 50 μm mean | Decades outdoors; sacrificial zinc layer | Nuts tapped oversize to suit; suitable to class 8.8, 10.9 only with controlled pickling and baking, not for 12.9; standard for structural and galvanised steelwork |
| Zinc flake (Geomet® / Dacromet® type) | ISO 10683 / ASTM F1136 | 8 – 12 μm | 600 to 1000 h salt spray | Non-electrolytic, so no hydrogen embrittlement: the recommended finish for 10.9 and 12.9; integral lubricant gives a controlled friction coefficient; silver or black |
| Zinc-nickel electroplate | ASTM B841 / ISO 19598 | 8 – 15 μm (12 – 15 % Ni) | 720 to 1000 h salt spray to red rust | Automotive and defence specification; high temperature stability; cadmium replacement |
| PTFE / Xylan® fluoropolymer | Applied over phosphate or zinc; colour to spec | 20 – 30 μm | Up to 3000 h salt spray with zinc base | Friction coefficient 0.08 to 0.12, no galling, easy break-out after years subsea; standard on B7 / L7 flange bolting offshore; blue, green, black, yellow |
| Cadmium plate, chromated | AMS-QQ-P-416 / ASTM F1941 | 5 – 13 μm | Marine and aerospace; galvanically compatible with aluminium | Aerospace and defence only; restricted under REACH / RoHS for general industry |
| Pickled & passivated (stainless) | ASTM A967 / A380 | — | Restores the chromium oxide film after forging and rolling | Standard on all stainless, duplex and nickel alloy hex bolts; supply with nickel or molybdenum-disulphide anti-seize to prevent thread galling |
Guide values calculated by the VDI 2230 method for coarse-thread hex bolts with the head bearing on a medium clearance hole, 90 % utilisation of the minimum yield strength, and equal thread and underhead friction μ = 0.14 (lightly oiled, phosphated or plain steel). Friction dominates: a PTFE-coated bolt at μ = 0.10 needs about 25 % less torque for the same preload, a dry stainless bolt at μ = 0.20 needs more and may gall. Validate for the joint before use.
FM = 0.9 · Rp0.2 · A0 / √(1 + 3[2 (d2/d0)(P/πd2 + 1.155 μG)]²); MA = FM(0.16 P + 0.58 d2 μG + μK DKm/2), DKm = (s + dh)/2.
| Size | FM 8.8 kN | MA 8.8 N·m | FM 10.9 kN | MA 10.9 N·m | FM 12.9 kN | MA 12.9 N·m |
|---|---|---|---|---|---|---|
| M6 | 9.0 | 11 | 13.2 | 16 | 15.5 | 18 |
| M8 | 16.5 | 26 | 24.3 | 38 | 28.4 | 44 |
| M10 | 26.3 | 50 | 38.7 | 74 | 45.2 | 87 |
| M12 | 38.4 | 87 | 56.4 | 128 | 66.0 | 149 |
| M14 | 52.7 | 139 | 77.4 | 204 | 90.6 | 238 |
| M16 | 72.6 | 215 | 106.6 | 316 | 124.7 | 370 |
| M18 | 90.9 | 307 | 129.5 | 437 | 151.6 | 511 |
| M20 | 116.9 | 434 | 166.5 | 618 | 194.9 | 723 |
| M22 | 146.2 | 597 | 208.2 | 850 | 243.6 | 995 |
| M24 | 168.4 | 748 | 239.8 | 1065 | 280.6 | 1246 |
| M27 | 221.8 | 1109 | 315.9 | 1579 | 369.6 | 1848 |
| M30 | 269.5 | 1503 | 383.8 | 2140 | 449.2 | 2505 |
| M33 | 336.1 | 2038 | 478.6 | 2903 | 560.1 | 3397 |
| M36 | 394.3 | 2619 | 561.5 | 3730 | 657.1 | 4365 |
FM is the assembly preload and MA the torque that produces it. For stainless A2-70 / A4-70 the yield is 450 MPa, so the figures scale to about 70 % of the 8.8 column below M16, and always use an anti-seize on stainless to keep friction predictable and prevent galling. Torque is not a substitute for a joint calculation; for flange bolting follow ASME PCC-1.
Flange, valve and wellhead bolting in A193 B7 / B7M, L7, Inconel 625 and super duplex; NACE MR0175 sour service; PTFE-coated for subsea break-out.
Reactor, column and heat exchanger bolting in Hastelloy C-276, Incoloy 825, Alloy 20, 904L and 316L where acids, chlorides or sulphur compounds attack carbon steel.
Turbine casing, steam line and boiler bolting in B16, B7, A-286, Inconel 718 and Nimonic 80A for sustained load at 400 to 650 °C; A320 L7 for LNG and cryogenic plant.
Seawater pumps, RO skids, hull and deck fittings in A4-80, super duplex 2507, Monel 400 / K-500, silicon bronze and titanium; immune to chloride pitting and SCC.
Hot-dip galvanised 8.8 and 10.9, F3125 A325 / A490 and EN 14399 HV bolts for bridges, towers, pre-engineered buildings, solar and wind foundations.
Fine pitch 10.9 and 12.9 for engines, gearboxes, hydraulics and bogies; zinc flake or zinc-nickel finished to OEM drawings with full dimensional reports.
| Test | Method | Applied to |
|---|---|---|
| Chemical analysis / PMI | OES on bar; XRF PMI on finished bolts | Every heat; 100 % of stainless and nickel alloy lots |
| Tensile, yield, elongation, RA | ISO 898-1 / ASTM F606 / ASTM A370 | Every heat-treatment lot; full-size wedge tensile where the standard requires |
| Proof load | ISO 898-1 / ASTM F606 | Classes 8.8 and above, A193, A320, F3125 |
| Hardness | Rockwell, Brinell or Vickers; surface and core | Every lot; decarburisation check on 10.9 / 12.9 |
| Charpy V-notch impact | ASTM A370 / ISO 148, −46 to −196 °C | A320 L7 / L7M / L43 / B8, duplex and nickel alloys on request |
| Thread & dimensions | Go / no-go gauges to ISO 1502 / ASME B1.2; micrometer, height gauge, profile projector | Every lot, sampled to ISO 3269 / ASME B18.18 |
| Microstructure & grain size | ASTM E112; ferrite count on duplex; sensitisation A262 on austenitics | Nickel alloys, duplex, A193 B8 class 2 and on request |
| Non-destructive testing | Magnetic particle, dye penetrant or ultrasonic | Large diameter and critical-service bolts on request |
| Coating thickness & salt spray | Magnetic / eddy current gauge; ASTM B117 | All plated, galvanised and coated lots |
Tell us the standard, size, length, grade and quantity. Our technical sales engineers respond within 2 to 4 business hours with certified pricing and lead times.