Home » DIN 7991 Specifications

DIN 7991 Specifications

Technical and Specification Summary of DIN 7991 Hexagon Socket Countersunk Head Cap Screws

1. Product Overview

  • Grade A Hexagon socket countersunk head cap screws with ISO metric thread, sizes ranging from M3 to M24.

  • Suitable for general mechanical connections, not recommended for applications with high axial preload.

2. Main Technical Parameters

  • Thread sizes: M3, M4, M5, M6, M8, M10, M12, (M14), M16, (M18), M20, (M22), M24.

  • Head shape: Countersunk design with a head angle of 90° (60° for some sizes).

  • Hexagon socket size (s value) and head height (k value) refer to the dimension table.

  • Shank length (l) covers a wide range, from 8 mm to over 100 mm, available in 10 mm or 20 mm increments.

  • Thread length (b) varies by size, calculated as:

3. Material and Mechanical Properties

  • Steel screws: Property class 8.8, hardness requirements:

    • ≤ M16: HV 250–320

    • > M16: HV 255–335

  • Steel screws: Property class 10.9, hardness requirements:

    • ≤ M16: HV 320–380

    • > M16: HV 325–385

  • Stainless steel screws: A2-70 for ≤ M20, A2-50 for > M20.

  • Non-ferrous metal screws: Typically copper-zinc alloy (e.g., CU2, CU3).

  • Surface treatment:

    • Steel: Black oxide finish

    • Stainless steel / non-ferrous metals: Bright finish

    • Electroplating or other protective coatings must be agreed upon when ordering.

4. Usage Considerations

  • Not recommended for high preload applications, as the critical cross-section is located under the hexagon socket, not at the thread.

  • When using a DIN 911 double-eccentric screwdriver, the preload force should not exceed 80% of the standard value for class 8.8 screws.

  • Certain sizes (in parentheses) and intermediate lengths should be avoided if possible.

  • Long screws (beyond the dashed-line indicated length) are fully threaded.

5. Quality Control and Inspection

  • Thread tolerance class: 6g

  • Product grade: A

  • Acceptance inspection includes hardness testing (for class 8.8 steel screws).

  • Surface roughness, plating quality, etc., shall comply with the relevant sections of DIN 267.

6. Marking and Nomenclature Example

  • Example: Hexagon socket countersunk head cap screw DIN 7991 — M12×60 — 8.8

  • If no property class is specified, the default supply grade is 8.8.



DIN 7991
Replaced by ISO 10642
Hexagon socket countersunk head screws

DIN 7991 Specifications

Screw Thread Technical Specifications
Screw Thread M3 M4 M5 M6
d
P Pitch 0.5 0.7 0.8 1
α tol.(+2) 90° 90° 90° 90°
Length of Thread L≤125 12 14 16 18
b 125＜L ≤ 200 / / / 24
L＞200 / / / /
dk max=nominal size 6 8 10 12
min 5.7 7.64 9.64 11.57
ds max=nominal size 3 4 5 6
min 2.86 3.82 4.82 5.82
e min 2.3 2.87 3.44 4.58
k max 1.7 2.3 2.8 3.3
s Nominal Size 2 2.5 3 4
min 2.02 2.52 3.02 4.02
max 2.1 2.6 3.1 4.12
t max=nominal size 1.2 1.8 2.3 2.5
min 0.95 1.55 2.05 2.25
Screw Thread M8 M10 M12 (M14)
d
P Pitch 1.25 1.5 1.75 2
α tol.(+2) 90° 90° 90° 90°
Length of Thread L≤125 22 26 30 34
b 125＜L ≤ 200 28 32 36 40
L＞200 / 45 49 53
dk max=nominal size 16 20 24 27
min 15.57 19.48 23.48 26.48
ds max=nominal size 8 10 12 14
min 7.78 9.78 11.73 13.73
e min 5.72 6.86 9.15 11.43
k max 4.4 5.5 6.5 7
s Nominal Size 5 6 8 10
min 5.02 6.02 8.025 10.025
max 5.14 6.14 8.175 10.175
t max=nominal size 3.5 4.4 4.6 4.8
min 3.2 4.1 4.3 4.5
Screw Thread M16 (M18) M20 M24
d
P Pitch 2 2.5 2.5 3
α tol.(+2) 90° 90° 90° 60°
Length of Thread L≤125 38 42 46 54
b 125＜L ≤ 200 44 48 52 60
L＞200 57 61 65 73
dk max=nominal size 30 33 36 39
min 29.48 32.38 35.38 38.38
ds max=nominal size 16 18 20 24
min 15.73 17.73 19.67 23.67
e min 11.43 13.72 13.72 16
k max 7.5 8 8.5 14
s Nominal Size 10 12 12 14
min 10.025 12.032 12.032 14.032
max 10.175 12.212 12.212 14.212
t max=nominal size 5.3 5.5 5.9 10.3
min 5 5.2 5.6 9.87