Thread rolling screws countersunk head, cross recessed metric thread

The standard specifies the characteristics of hexagon head thread forming screws for connections. This type of threaded connection, if the screw is not replaced, offers a good tear resistance, since the clearance between the screw and nut is equal to zero. In addition, the friction between mating parts further increases the unscrewing torque. For the preparation of the holes diameters see UNI 8108.

Dimensional Drawing and Technical Diagrams

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Key Dimensions and Technical Parameters

Dimensions in mm - source UNI 8113

Publication date: 1993

d thread size M 2 M 2.2 M 2.5 M 3 M 3.5 M 4 M 5 M 6 M 8
P 0.4 0.45 0.45 0.5 0.6 0.7 0.8 1 1.25
D max 3.8 4.3 4.7 5.6 6.5 7.5 9.2 11 14.5
D min 3.5 4 4.4 5.3 6.14 7.14 8.84 10.57 14.07
k max 1.2 1.3 1.5 1.65 1.93 2.2 2.5 3 4
r ≈ 0.2 0.25 0.25 0.3 0.35 0.4 0.5 0.6 0.8
Z recess nr 1 1 1 1 2 2 2 3 4
m ≈ 2.4 2.4 2.8 3 4 4.2 4.4 6.1 8.5
max depth 1.35 1.35 1.73 2.01 2.06 2.31 2.51 2.92 4.38
min depth 1.1 1.1 1.48 1.76 1.6 1.85 2.05 2.46 3.86
H recess nr 1 1 1 1 2 2 2 3 4
m ≈ 2.5 2.5 2.7 2.9 3.9 4.4 4.6 6.6 8.7
max depth 1.32 1.32 1.55 1.8 1.9 2.4 2.6 3.3 4.4
min depth 1.02 1.02 1.25 1.5 1.4 1.9 2.1 2.8 3.9

UNI 8113 ≈ commercial items

d thread size M 2 M 2.2 M 2.5 M 3 M 3.5 M 4 M 5 M 6 M 8
nominal length l
6 X X X
8 X X X X
10 X X X X X X X
12 X X X X X X X
14 X X X X X X X X
16 X X X X X X X X X
20 X X X X X X X
25 X X X X X X X
30 X X X X X X
35 X X X X
40 X X X X
45 X X X
50 X X X