DIN 912 socket head cap screws
DIN 912 hexagon socket head cap screws, commonly known as Allen bolts, are among the most versatile fasteners in mechanical engineering. They define a metric bolt with a low head and hexagonal socket that allows high tightening torques and nearly flush mounting. Originally standardized under the German designation, since 2004 the international reference is ISO 4762, although the term DIN 912 continues to be widely used in industry. They are mostly manufactured in high-strength steel in grades 8.8, 10.9, and 12.9, and are used in tooling, molds, metal structures, and any application requiring a neat seating and high mechanical capacity.
Standard family
Section titled “Standard family”The original DIN 912 standard (Hexagon socket head cap screws) was developed by the Deutsches Institut für Normung and, until its withdrawal, constituted the reference technical document for this type of fastener in the metric system. It has now been replaced by the international standard ISO 4762:2004 “Hexagon socket head cap screws” (and its European transcription EN ISO 4762), which maintains complete dimensional interchangeability. In parallel, in the American market there is the ASME B18.3.2M standard for metric hexagon socket head cap screws, dimensionally equivalent to ISO 4762. The old DIN 912 designation is retained due to tradition and because many distributors and customers still identify the product by that name.
Dimensions
Section titled “Dimensions”The main dimensions of metric DIN 912 bolts with normal (coarse) pitch and standard strength grade are given in the following table. The thread length indicated corresponds to the range of bolts with nominal length L ≤ 125 mm; for longer lengths, consult the full standard.
| Nominal diameter | Pitch | Head diameter (dk) | Head height (k) | Hexagon socket size (s) | Minimum thread length (b)¹ |
|---|---|---|---|---|---|
| M3 / 0.118 in | 0,5 mm / 0.0197 in | 5,5 mm / 0.217 in | 3,0 mm / 0.118 in | 2,5 mm / 0.098 in | 18 mm / 0.71 in |
| M4 / 0.157 in | 0,7 mm / 0.0276 in | 7,0 mm / 0.276 in | 4,0 mm / 0.157 in | 3,0 mm / 0.118 in | 20 mm / 0.79 in |
| M5 / 0.197 in | 0,8 mm / 0.0315 in | 8,5 mm / 0.335 in | 5,0 mm / 0.197 in | 4,0 mm / 0.157 in | 22 mm / 0.87 in |
| M6 / 0.236 in | 1,0 mm / 0.0394 in | 10,0 mm / 0.394 in | 6,0 mm / 0.236 in | 5,0 mm / 0.197 in | 24 mm / 0.94 in |
| M8 / 0.315 in | 1,25 mm / 0.0492 in | 13,0 mm / 0.512 in | 8,0 mm / 0.315 in | 6,0 mm / 0.236 in | 28 mm / 1.10 in |
| M10 / 0.394 in | 1,5 mm / 0.0591 in | 16,0 mm / 0.630 in | 10,0 mm / 0.394 in | 8,0 mm / 0.315 in | 32 mm / 1.26 in |
| M12 / 0.472 in | 1,75 mm / 0.0689 in | 18,0 mm / 0.709 in | 12,0 mm / 0.472 in | 10,0 mm / 0.394 in | 36 mm / 1.42 in |
| M14 / 0.551 in | 2,0 mm / 0.0787 in | 21,0 mm / 0.827 in | 14,0 mm / 0.551 in | 12,0 mm / 0.472 in | 40 mm / 1.57 in |
| M16 / 0.630 in | 2,0 mm / 0.0787 in | 24,0 mm / 0.945 in | 16,0 mm / 0.630 in | 14,0 mm / 0.551 in | 44 mm / 1.73 in |
| M20 / 0.787 in | 2,5 mm / 0.0984 in | 30,0 mm / 1.181 in | 20,0 mm / 0.787 in | 17,0 mm / 0.669 in | 52 mm / 2.05 in |
| M24 / 0.945 in | 3,0 mm / 0.1181 in | 36,0 mm / 1.417 in | 24,0 mm / 0.945 in | 19,0 mm / 0.748 in | 60 mm / 2.36 in |
¹ For nominal lengths L > 125 mm, the thread length b must be calculated according to the standard relationship.
Tightening torque table
Section titled “Tightening torque table”The recommended tightening torques below are valid for bolts assembled dry (friction coefficient µ ≈ 0.14) without additional lubrication. With lubricated surfaces or self-lubricating coatings, the torque should be reduced by 15-25%.
| Diameter x pitch | Grade 8.8 N·m / lb-ft | Grade 10.9 N·m / lb-ft | Grade 12.9 N·m / lb-ft |
|---|---|---|---|
| M3 x 0,5 | 1,0 / 0.74 | 1,5 / 1.11 | 1,8 / 1.33 |
| M4 x 0,7 | 2,2 / 1.62 | 3,2 / 2.36 | 3,8 / 2.80 |
| M5 x 0,8 | 4,5 / 3.32 | 6,5 / 4.80 | 7,7 / 5.68 |
| M6 x 1,0 | 7,6 / 5.61 | 11,0 / 8.11 | 13,0 / 9.59 |
| M8 x 1,25 | 25,0 / 18.44 | 35,0 / 25.81 | 42,0 / 30.98 |
| M10 x 1,5 | 49,0 / 36.14 | 70,0 / 51.63 | 85,0 / 62.70 |
| M12 x 1,75 | 85,0 / 62.70 | 120,0 / 88.52 | 145,0 / 106.96 |
| M14 x 2,0 | 135,0 / 99.58 | 190,0 / 140.16 | 230,0 / 169.65 |
| M16 x 2,0 | 210,0 / 154.91 | 300,0 / 221.30 | 360,0 / 265.56 |
| M20 x 2,5 | 400,0 / 295.07 | 570,0 / 420.47 | 680,0 / 501.61 |
| M24 x 3,0 | 680,0 / 501.61 | 960,0 / 708.16 | 1150,0 / 848.29 |
Drill sizes
Section titled “Drill sizes”The table includes the drill diameter for clearance hole with medium fit (according to ISO 273, free fit) and the tap drill for the nut or blind hole corresponding to the coarse metric thread. Always use the tap drill appropriate for the thread pitch of the bolt.
| Nominal diameter | Clearance drill (medium fit) mm / in | Tap drill (metric) mm / in |
|---|---|---|
| M3 | 3,4 mm / 0.134 in | 2,5 mm / 0.098 in |
| M4 | 4,5 mm / 0.177 in | 3,3 mm / 0.130 in |
| M5 | 5,5 mm / 0.217 in | 4,2 mm / 0.165 in |
| M6 | 6,6 mm / 0.260 in | 5,0 mm / 0.197 in |
| M8 | 9,0 mm / 0.354 in | 6,8 mm / 0.268 in |
| M10 | 11,0 mm / 0.433 in | 8,5 mm / 0.335 in |
| M12 | 13,5 mm / 0.531 in | 10,2 mm / 0.402 in |
| M14 | 15,5 mm / 0.610 in | 12,0 mm / 0.472 in |
| M16 | 17,5 mm / 0.689 in | 14,0 mm / 0.551 in |
| M20 | 22,0 mm / 0.866 in | 17,5 mm / 0.689 in |
| M24 | 26,0 mm / 1.024 in | 21,0 mm / 0.827 in |
Load capacities
Section titled “Load capacities”The maximum permissible loads are calculated from the tensile stress area of the metric thread (As per ISO 724) and the minimum yield strength of the grade (Rp0.2). The direct tensile load and single shear strength are indicated (without considering additional safety factors). For calculation in actual connections, the corresponding safety factors must be applied according to the standard or design guideline used.
| Diameter | Grade 8.8 (tensile) kN / lbf | Grade 8.8 (shear) kN / lbf | Grade 10.9 (tensile) kN / lbf | Grade 10.9 (shear) kN / lbf | Grade 12.9 (tensile) kN / lbf | Grade 12.9 (shear) kN / lbf |
|---|---|---|---|---|---|---|
| M3 | 3,22 / 724 | 1,93 / 434 | 4,53 / 1 019 | 2,72 / 611 | 5,43 / 1 221 | 3,26 / 733 |
| M4 | 5,62 / 1 263 | 3,37 / 758 | 7,90 / 1 776 | 4,74 / 1 066 | 9,48 / 2 131 | 5,69 / 1 279 |
| M5 | 9,09 / 2 044 | 5,45 / 1 225 | 12,78 / 2 874 | 7,67 / 1 724 | 15,34 / 3 449 | 9,20 / 2 068 |
| M6 | 12,86 / 2 891 | 7,72 / 1 735 | 18,09 / 4 067 | 10,85 / 2 439 | 21,71 / 4 881 | 13,03 / 2 929 |
| M8 | 23,42 / 5 265 | 14,05 / 3 159 | 32,94 / 7 405 | 19,76 / 4 443 | 39,53 / 8 887 | 23,72 / 5 333 |
| M10 | 37,12 / 8 345 | 22,27 / 5 007 | 52,20 / 11 735 | 31,32 / 7 041 | 62,64 / 14 082 | 37,58 / 8 448 |
| M12 | 53,95 / 12 129 | 32,37 / 7 278 | 75,87 / 17 059 | 45,52 / 10 235 | 91,04 / 20 470 | 54,62 / 12 280 |
| M16 | 100,48 / 22 589 | 60,29 / 13 553 | 141,30 / 31 764 | 84,78 / 19 058 | 169,56 / 38 117 | 101,74 / 22 870 |
| M20 | 156,80 / 35 253 | 94,08 / 21 152 | 220,50 / 49 571 | 132,30 / 29 743 | 264,60 / 59 485 | 158,76 / 35 691 |
| M24 | 225,92 / 50 783 | 135,55 / 30 470 | 317,70 / 71 410 | 190,62 / 42 846 | 381,24 / 85 692 | 228,74 / 51 415 |
Standard equivalences
Section titled “Standard equivalences”The following table summarizes the correspondence and standard evolution of the hexagon socket head cap screw. All versions maintain interchangeable external dimensions.
| Designation | Standard |
|---|---|
| Original (Germany) | DIN 912 |
| Current international | ISO 4762:2004 |
| European | EN ISO 4762 |
| American (metric) | ASME B18.3.2M |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the difference between DIN 912 and ISO 4762?
Section titled “What is the difference between DIN 912 and ISO 4762?”The DIN 912 standard was the original German specification and has been replaced by ISO 4762. From a dimensional point of view, they are identical: the same head dimensions, hexagon socket, lengths, and threads. ISO unifies international criteria and may incorporate small updates in tolerances or marking, but bolts complying with either standard are completely interchangeable.
Which strength grade should I choose for a DIN 912 bolt?
Section titled “Which strength grade should I choose for a DIN 912 bolt?”It depends on the mechanical load. In general fastening applications, grade 8.8 is used. For high-strength joints, such as tooling and molds, grade 10.9 is the most common. Grade 12.9 is reserved for cases where maximum load capacity is needed, but it is more brittle under impacts and requires strict control of the tightening torque.
How is the total length of a DIN 912 bolt measured?
Section titled “How is the total length of a DIN 912 bolt measured?”The nominal length is measured from the base of the head (bearing surface) to the end of the shank. The head height is not included. A DIN 912 M8 x 30 bolt has 30 mm of useful shank under the head.
What is the recommended tightening torque for an M8 DIN 912 grade 10.9 bolt?
Section titled “What is the recommended tightening torque for an M8 DIN 912 grade 10.9 bolt?”Under dry tightening conditions (µ ≈ 0.14), the recommended torque for M8 x 1.25 grade 10.9 is 35 N·m (25.8 lb-ft). If the bolt is installed lubricated, this value should be reduced by approximately 20-25%.
Can a DIN 912 bolt be replaced by a socket head cap screw per ANSI B18.3?
Section titled “Can a DIN 912 bolt be replaced by a socket head cap screw per ANSI B18.3?”ANSI/ASME B18.3 bolts for inch threads (UNC/UNF) are not directly interchangeable with DIN 912 metric pitch bolts, since both the thread and the hexagon socket may differ. However, the ASME B18.3.2M standard exists, which defines metric hexagon socket head cap screws and is equivalent to ISO 4762 and therefore to the old DIN 912, maintaining full dimensional interchangeability.
Do I need to countersink the bearing surface for a DIN 912 bolt?
Section titled “Do I need to countersink the bearing surface for a DIN 912 bolt?”A conical countersink is not necessary, because the head of the DIN 912 is cylindrical and flat on its bearing face. However, ensure that the seating surface is flat and perpendicular to the axis of the threaded hole. If the head is to be fully recessed, use a cylindrical counterbore with the diameter corresponding to the head (dk).
Sources Consulted
Section titled “Sources Consulted”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/metric-bolt-head-wrench-size-d_1458.html
- mcmaster.com: https://www.mcmaster.com/products/din-912-socket-head-cap-screws