ISO DIN fastener equivalences
International standardization has made it possible to harmonize the specifications of fasteners, and it is common to find DIN standards alongside their ISO or ANSI equivalents. For example, a partially threaded hex head bolt M12 × 1,75 mm / 0.069 in under DIN 931 directly corresponds to ISO 4014, maintaining practically identical dimensions and mechanical properties.
Standard equivalences for fasteners
Section titled “Standard equivalences for fasteners”| DIN standard | Equivalent ISO standard | Related ANSI/ASME standard | Description |
|---|---|---|---|
| DIN 931 | ISO 4014 | ASME B18.2.1 (UNC/UNF thread) | Partially threaded hex head bolt |
| DIN 933 | ISO 4017 | ASME B18.2.1 (UNC/UNF thread) | Fully threaded hex head bolt |
| DIN 934 | ISO 4032 | ASME B18.2.2 | Regular hex nut |
| DIN 912 | ISO 4762 | ASME B18.3 | Socket head cap screw (Allen) |
| DIN 7991 | ISO 10642 | ASME B18.3 (flat head Allen) | Countersunk head socket screw |
| DIN 125 | ISO 7089 | ASME B18.22.1 | Chamfered flat washer |
| DIN 127 | ISO 7090 | ASME B18.21.1 | Spring lock washer (Grower) |
| DIN 985 | ISO 10511 | — | Low hex lock nut with polyamide ring |
| DIN 6921 | ISO 16613 | ASME B18.2.1 (flange bolt) | Hex head bolt with flange |
| DIN 580 | ISO 3266 | — | Threaded lifting eye bolt |
| DIN 444 | ISO 2340 | — | Eye bolt |
Dimensions and designation of ISO metric threads
Section titled “Dimensions and designation of ISO metric threads”The ISO metric thread according to ISO 68-1 and ISO 724 defines 60° profiles with coarse and fine pitch. The following table lists the most commonly used combinations in industrial fasteners.
| Nominal diameter (mm / in) | Coarse pitch (mm / in) | Fine pitch (mm / in) | Tap drill for coarse pitch (mm / in) |
|---|---|---|---|
| M3 / 0.118 in | 0,5 / 0.020 in | — | 2,5 / 0.098 in |
| M4 / 0.157 in | 0,7 / 0.028 in | — | 3,3 / 0.130 in |
| M5 / 0.197 in | 0,8 / 0.031 in | 0,5 / 0.020 in | 4,2 / 0.165 in |
| M6 / 0.236 in | 1,0 / 0.039 in | 0,75 / 0.030 in | 5,0 / 0.197 in |
| M8 / 0.315 in | 1,25 / 0.049 in | 1,0 / 0.039 in | 6,8 / 0.268 in |
| M10 / 0.394 in | 1,5 / 0.059 in | 1,25 / 0.049 in | 8,5 / 0.335 in |
| M12 / 0.472 in | 1,75 / 0.069 in | 1,25 / 0.049 in | 10,2 / 0.402 in |
| M14 / 0.551 in | 2,0 / 0.079 in | 1,5 / 0.059 in | 12,0 / 0.472 in |
| M16 / 0.630 in | 2,0 / 0.079 in | 1,5 / 0.059 in | 14,0 / 0.551 in |
| M18 / 0.709 in | 2,5 / 0.098 in | 1,5 / 0.059 in | 15,5 / 0.610 in |
| M20 / 0.787 in | 2,5 / 0.098 in | 1,5 / 0.059 in | 17,5 / 0.689 in |
| M22 / 0.866 in | 2,5 / 0.098 in | 1,5 / 0.059 in | 19,5 / 0.768 in |
| M24 / 0.945 in | 3,0 / 0.118 in | 2,0 / 0.079 in | 21,0 / 0.827 in |
| M27 / 1.063 in | 3,0 / 0.118 in | 2,0 / 0.079 in | 24,0 / 0.945 in |
| M30 / 1.181 in | 3,5 / 0.138 in | 2,0 / 0.079 in | 26,5 / 1.043 in |
Allowable loads for metric bolts
Section titled “Allowable loads for metric bolts”Proof load values according to ISO 898-1 for the most common strength classes. Loads correspond to assembly without additional lubrication and are based on the nominal tensile stress area.
| Nominal diameter (mm / in) | Tensile stress area (mm² / in²) | Allowable load class 8.8 (kN / lbf) | Allowable load class 10.9 (kN / lbf) | Allowable load class 12.9 (kN / lbf) |
|---|---|---|---|---|
| M6 / 0.236 in | 20,1 / 0.0312 in² | 11,7 / 2 630 | 16,7 / 3 750 | 19,5 / 4 380 |
| M8 / 0.315 in | 36,6 / 0.0567 in² | 21,2 / 4 770 | 30,4 / 6 830 | 35,5 / 7 980 |
| M10 / 0.394 in | 58,0 / 0.0899 in² | 33,6 / 7 560 | 48,1 / 10 800 | 56,3 / 12 660 |
| M12 / 0.472 in | 84,3 / 0.1307 in² | 48,9 / 11 000 | 70,0 / 15 700 | 81,8 / 18 390 |
| M14 / 0.551 in | 115 / 0.1782 in² | 66,7 / 15 000 | 95,5 / 21 450 | 111,6 / 25 090 |
| M16 / 0.630 in | 157 / 0.2432 in² | 91,1 / 20 470 | 130,3 / 29 300 | 152,3 / 34 240 |
| M18 / 0.709 in | 192 / 0.2976 in² | 111,4 / 25 040 | 159,4 / 35 840 | 186,2 / 41 860 |
| M20 / 0.787 in | 277 / 0.4290 in² | 160,7 / 36 120 | 229,9 / 51 680 | 268,7 / 60 410 |
| M22 / 0.866 in | 333 / 0.5162 in² | 193,1 / 43 420 | 276,4 / 62 130 | 323,0 / 72 610 |
| M24 / 0.945 in | 353 / 0.5472 in² | 204,7 / 46 030 | 293,0 / 65 870 | 342,4 / 76 970 |
Recommended tightening torques
Section titled “Recommended tightening torques”Indicative values for coarse metric thread bolts, dry assembly (without lubricant). The friction factor considered is μ ≈ 0,12. Always verify manufacturer specifications for critical applications.
| Diameter (mm / in) | Class 8.8 (N·m / lb·ft) | Class 10.9 (N·m / lb·ft) | Class 12.9 (N·m / lb·ft) |
|---|---|---|---|
| M6 / 0.236 in | 10 / 7.4 | 14 / 10.3 | 17 / 12.5 |
| M8 / 0.315 in | 25 / 18.4 | 35 / 25.8 | 41 / 30.2 |
| M10 / 0.394 in | 49 / 36 | 69 / 51 | 81 / 60 |
| M12 / 0.472 in | 85 / 63 | 120 / 89 | 140 / 103 |
| M14 / 0.551 in | 135 / 100 | 190 / 140 | 220 / 162 |
| M16 / 0.630 in | 210 / 155 | 295 / 218 | 345 / 254 |
| M18 / 0.709 in | 290 / 214 | 405 / 299 | 475 / 350 |
| M20 / 0.787 in | 410 / 302 | 575 / 424 | 670 / 494 |
| M22 / 0.866 in | 550 / 406 | 770 / 568 | 900 / 664 |
| M24 / 0.945 in | 710 / 524 | 995 / 734 | 1 160 / 856 |
Tap drills for metric threads
Section titled “Tap drills for metric threads”Drill diameters for pre-drilling before manual or machine tapping with a tap. Values correspond to ISO metric coarse thread, suitable for short-chip materials.
| Thread | Pitch (mm / in) | Drill diameter (mm / in) |
|---|---|---|
| M3 | 0,5 / 0.020 | 2,5 / 0.098 |
| M4 | 0,7 / 0.028 | 3,3 / 0.130 |
| M5 | 0,8 / 0.031 | 4,2 / 0.165 |
| M6 | 1,0 / 0.039 | 5,0 / 0.197 |
| M8 | 1,25 / 0.049 | 6,8 / 0.268 |
| M10 | 1,5 / 0.059 | 8,5 / 0.335 |
| M12 | 1,75 / 0.069 | 10,2 / 0.402 |
| M14 | 2,0 / 0.079 | 12,0 / 0.472 |
| M16 | 2,0 / 0.079 | 14,0 / 0.551 |
| M18 | 2,5 / 0.098 | 15,5 / 0.610 |
| M20 | 2,5 / 0.098 | 17,5 / 0.689 |
| M22 | 2,5 / 0.098 | 19,5 / 0.768 |
| M24 | 3,0 / 0.118 | 21,0 / 0.827 |
For fine pitches, it is recommended to subtract the pitch from the nominal diameter: drill (mm) ≈ nominal diameter – pitch.
Head marking according to ISO and DIN
Section titled “Head marking according to ISO and DIN”The marking of metric bolts and nuts is regulated by ISO 898-1 (bolts) and ISO 898-2 (nuts). The head must bear at least the strength class and the manufacturer’s identification.
| Strength class | Head marking (symbols) | Characteristic material | Tensile strength Rm (MPa / ksi) | Yield strength Re (MPa / ksi) |
|---|---|---|---|---|
| 4.6 | 4.6 | Low carbon steel | 400 / 58 | 240 / 34.8 |
| 5.6 | 5.6 | Low/medium carbon steel | 500 / 72.5 | 300 / 43.5 |
| 8.8 | 8.8 | Medium carbon steel quenched and tempered | 800 / 116 | 640 / 92.8 |
| 10.9 | 10.9 | Alloy steel quenched and tempered | 1 000 / 145 | 900 / 130 |
| 12.9 | 12.9 | Alloy steel quenched and tempered | 1 200 / 174 | 1 080 / 156 |
| A2-70 | A2-70 | Austenitic stainless steel (AISI 304) | 700 / 101.5 | 450 / 65.3 |
| A4-80 | A4-80 | Austenitic stainless steel with Mo (AISI 316) | 800 / 116 | 600 / 87.0 |
Nuts are marked on one of the bearing faces (usually the one in contact with the washer) indicating the strength class by a numerical code (e.g., 8, 10, 12) and, in some cases, an identification dot or groove.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the standard pitch for an M12 coarse thread bolt?
Section titled “What is the standard pitch for an M12 coarse thread bolt?”The ISO coarse pitch for M12 is 1,75 mm / 0.069 in, with a recommended tap drill diameter of 10,2 mm / 0.402 in.
What tightening torque does a dry mounted M10 class 10.9 bolt require?
Section titled “What tightening torque does a dry mounted M10 class 10.9 bolt require?”A tightening torque of approximately 69 N·m / 51 lb·ft is recommended for an M10 class 10.9 with coarse thread and no lubrication.
How many kilonewtons can an M16 grade 8.8 bolt withstand before yielding?
Section titled “How many kilonewtons can an M16 grade 8.8 bolt withstand before yielding?”An M16 class 8.8 bolt supports a proof load of 91,1 kN / 20 470 lbf, based on a tensile stress area of 157 mm² / 0.243 in².
What drill bit is needed to make an M8 coarse thread?
Section titled “What drill bit is needed to make an M8 coarse thread?”For threading M8 pitch 1,25 mm / 0.049 in, a drill bit of 6,8 mm / 0.268 in diameter is used; in hard materials it can be slightly increased up to 7,0 mm / 0.276 in.
Is a DIN 933 bolt interchangeable with ISO 4017?
Section titled “Is a DIN 933 bolt interchangeable with ISO 4017?”Yes, both standards define the same fully threaded hex head bolt with ISO metric thread; the thread length in DIN 933 may vary slightly in some old versions, but they are dimensionally compatible.
What is the closest ANSI equivalent to an M10 × 1,5 mm / 0.059 in metric bolt?
Section titled “What is the closest ANSI equivalent to an M10 × 1,5 mm / 0.059 in metric bolt?”There is no direct counterpart in metric thread within ANSI, but the closest inch hex head bolt per ASME B18.2.1 would be 3/8-16 UNC, whose pitch of 1,588 mm / 0.0625 in resembles the M10 coarse pitch; however, metric and imperial threads must never be mixed.