DIN 933 hex bolts
DIN 933 hex bolts are fasteners with full metric thread up to the head, designed according to DIN 933 (equivalent to ISO 4017). They are widely used in steel construction, mechanical engineering, and industrial applications. The hexagonal head allows tightening with a standard wrench, and the full thread facilitates assembly in nuts or tapped holes of greater thickness. Below are the dimensions, pitches, permissible loads, equivalences, and tightening torques for the most common diameters.
Dimensions
Section titled “Dimensions”The head and length dimensions comply with DIN 933 (traditional version) and are valid for carbon steel bolts with coarse metric thread.
| Nominal diameter | Width across flats (s) | Head height (k) | Standard lengths (L) |
|---|---|---|---|
| M5 | 8 mm / 0.315 in | 3,5 mm / 0.138 in | 10–50 mm / 0.394–1.969 in |
| M6 | 10 mm / 0.394 in | 4,0 mm / 0.157 in | 12–60 mm / 0.472–2.362 in |
| M8 | 13 mm / 0.512 in | 5,3 mm / 0.209 in | 16–80 mm / 0.630–3.150 in |
| M10 | 17 mm / 0.669 in | 6,4 mm / 0.252 in | 20–100 mm / 0.787–3.937 in |
| M12 | 19 mm / 0.748 in | 7,5 mm / 0.295 in | 25–120 mm / 0.984–4.724 in |
| M16 | 24 mm / 0.945 in | 10,0 mm / 0.394 in | 30–160 mm / 1.181–6.299 in |
| M20 | 30 mm / 1.181 in | 12,5 mm / 0.492 in | 40–200 mm / 1.575–7.874 in |
| M24 | 36 mm / 1.417 in | 15,0 mm / 0.591 in | 50–240 mm / 1.969–9.449 in |
| M30 | 46 mm / 1.811 in | 18,7 mm / 0.736 in | 60–300 mm / 2.362–11.811 in |
| M36 | 55 mm / 2.165 in | 22,5 mm / 0.886 in | 70–360 mm / 2.756–14.173 in |
Note: The currently effective ISO 4017 standard adopted reduced widths across flats for M10 (16 mm / 0.630 in), M12 (18 mm / 0.709 in) and M14 (21 mm / 0.827 in); however, the traditional DIN 933 version with the indicated measurements remains the most commercially supplied.
Thread and pitch
Section titled “Thread and pitch”The thread pitch follows the ISO 724 coarse series (normal pitch). The pitch, major diameter, and tensile stress area values are essential for mechanical dimensioning.
| Nominal diameter | Pitch (P) | Tensile stress area (Aₛ) |
|---|---|---|
| M5 | 0,8 mm / 0.031 in | 14,2 mm² / 0.022 in² |
| M6 | 1,0 mm / 0.039 in | 20,1 mm² / 0.031 in² |
| M8 | 1,25 mm / 0.049 in | 36,6 mm² / 0.057 in² |
| M10 | 1,5 mm / 0.059 in | 58,0 mm² / 0.090 in² |
| M12 | 1,75 mm / 0.069 in | 84,3 mm² / 0.131 in² |
| M16 | 2,0 mm / 0.079 in | 157 mm² / 0.243 in² |
| M20 | 2,5 mm / 0.098 in | 245 mm² / 0.380 in² |
| M24 | 3,0 mm / 0.118 in | 353 mm² / 0.547 in² |
| M30 | 3,5 mm / 0.138 in | 561 mm² / 0.870 in² |
| M36 | 4,0 mm / 0.157 in | 817 mm² / 1.266 in² |
The thread profile has a 60° angle and a depth equal to 0.54125 × P. The thread is fully metric per ISO 68-1 / ISO 724.
Permissible loads
Section titled “Permissible loads”Minimum proof loads for grade 8.8 bolts, calculated per ISO 898-1 (proof stress 580 MPa for M5–M16 and 600 MPa for M20–M36). Values in kN and lbf.
| Diameter | Proof load (kN) | Proof load (lbf) |
|---|---|---|
| M5 | 8,2 kN | 1 840 lbf |
| M6 | 11,7 kN | 2 630 lbf |
| M8 | 21,2 kN | 4 770 lbf |
| M10 | 33,6 kN | 7 560 lbf |
| M12 | 48,9 kN | 11 000 lbf |
| M16 | 91,1 kN | 20 500 lbf |
| M20 | 147 kN | 33 100 lbf |
| M24 | 212 kN | 47 700 lbf |
| M30 | 325 kN | 73 100 lbf |
| M36 | 474 kN | 106 600 lbf |
Note: For grade 10.9 multiply by ≈1.41; for 12.9 multiply by ≈1.72. Ultimate tensile strength is approx. 800 MPa (grade 8.8) and 1000 MPa (grade 10.9).
Standard equivalences
Section titled “Standard equivalences”DIN 933 bolts are dimensionally equivalent to the following international standards:
| Standard | Description | Equivalence |
|---|---|---|
| ISO 4017 | Hexagon head bolts with full thread | Total (same dimensions, with minor differences in width across flats for some sizes) |
| ANSI B18.2.3.1M | Metric hex head screws | Functional (the metric range is similar, although the American head design may vary slightly in underhead radii and heights) |
| EN 24017 | European version of ISO 4017 | Identical to ISO 4017 |
There is no direct inch equivalent; for UNC/UNF thread applications, it is recommended to use SAE J429 or ASME B18.2.1.
Tightening torque
Section titled “Tightening torque”Reference values for DIN 933 grade 8.8 bolts in dry threaded coupling (friction coefficient μ ≈ 0.12). Typical torque ranges are given in N·m and lb·pie. For lubricated assembly, reduce values by 25‑30 %.
| Diameter | Dry tightening torque (N·m) | Dry tightening torque (lb·pie) |
|---|---|---|
| M5 | 5,5 – 7,0 N·m | 4,1 – 5,2 lb·pie |
| M6 | 9,0 – 11 N·m | 6,6 – 8,1 lb·pie |
| M8 | 22 – 27 N·m | 16 – 20 lb·pie |
| M10 | 45 – 55 N·m | 33 – 41 lb·pie |
| M12 | 80 – 95 N·m | 59 – 70 lb·pie |
| M16 | 195 – 235 N·m | 144 – 173 lb·pie |
| M20 | 350 – 420 N·m | 258 – 310 lb·pie |
| M24 | 600 – 710 N·m | 443 – 524 lb·pie |
| M30 | 950 – 1100 N·m | 700 – 811 lb·pie |
| M36 | 1200 – 1400 N·m | 885 – 1033 lb·pie |
Note: Always verify the specific design tightening torque; values may vary depending on lubrication, joint material, and wrench accuracy.
Drill sizes for clearance hole and tapped hole
Section titled “Drill sizes for clearance hole and tapped hole”Based on ISO 724 recommendations and general workshop practice. Diameters in mm and in.
| Nominal diameter | Drill for clearance hole (medium) | Drill for tapping (tap) |
|---|---|---|
| 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 | 12,0 mm / 0.472 in | 8,5 mm / 0.335 in |
| M12 | 14,0 mm / 0.551 in | 10,2 mm / 0.402 in |
| M16 | 18,0 mm / 0.709 in | 14,0 mm / 0.551 in |
| M20 | 22,0 mm / 0.866 in | 17,5 mm / 0.689 in |
| M24 | 27,0 mm / 1.063 in | 21,0 mm / 0.827 in |
| M30 | 33,0 mm / 1.299 in | 26,5 mm / 1.043 in |
| M36 | 40,0 mm / 1.575 in | 32,0 mm / 1.260 in |
The clearance hole is for medium clearance assembly, suitable for most industrial applications. The tap drill diameter corresponds to standard coarse pitch.
Materials and finishes
Section titled “Materials and finishes”- Carbon steel: property classes 5.8, 8.8 and 10.9 per ISO 898‑1.
- Stainless steels: A2‑70 and A4‑80 (ISO 3506‑1).
- Common surface finishes: electrolytic zinc plating (silver or blue), chromate, hot-dip galvanizing (HDG), and nickel plating.
- Heat treatments: quenching and tempering for classes 8.8 and above.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the standard thread pitch for an M8 DIN 933 bolt?
Section titled “What is the standard thread pitch for an M8 DIN 933 bolt?”The ISO coarse pitch is 1,25 mm / 0.049 in; for M8 there are also fine pitches of 1,0 mm / 0.039 in and 0,75 mm / 0.030 in, but the standard supply for DIN 933 is 1,25 mm.
What is the minimum proof load of an M12 grade 8.8 bolt?
Section titled “What is the minimum proof load of an M12 grade 8.8 bolt?”An M12 grade 8.8 supports at least 48,9 kN / 11 000 lbf without permanent deformation, based on a tensile stress area of 84,3 mm² and proof stress of 580 MPa.
What is the width across flats of an M10 DIN 933 bolt?
Section titled “What is the width across flats of an M10 DIN 933 bolt?”The traditional measurement is 17 mm / 0.669 in; the current ISO 4017 standard specifies 16 mm / 0.630 in, although most commercial inventory still uses 17 mm.
What torque is recommended for an M6 8.8 in a dry joint?
Section titled “What torque is recommended for an M6 8.8 in a dry joint?”A tightening torque of 9,0 to 11 N·m / 6.6 to 8.1 lb·pie is recommended; with light lubrication, reduce by approximately 30%.
What clearance hole drill does an M16 bolt need?
Section titled “What clearance hole drill does an M16 bolt need?”For a medium clearance hole, use a 18 mm / 0.709 in drill; the fine pitch diameter would require a tap drill of 14 mm / 0.551 in.
Which American standard can a DIN 933 bolt be interchanged with?
Section titled “Which American standard can a DIN 933 bolt be interchanged with?”There is no direct inch replacement; the metric standard ANSI B18.2.3.1M defines hex head screws dimensionally similar to DIN 933 / ISO 4017.