Effective Length of thread engagement
External thread fastener:
Thread - steel grade
M1
M1.2
M1.6
M2
M3
M4
M5
M6
M8
M10
M12
M14
M16
M20
M24
M30
-
3.6
4.6
4.8
5.6
5.8
6.8
8.8
9.8
10.9
12.9
Ratio of shear strength to tensile strength τ/σ
(steel)
Internal thread tapped hole:
Tensile strength σ
MPa
Ratio of shear strength to tensile strength τ/σ
(cast iron)
tensile stress area A
t
=π/4 d
0
2
; d
0
=(d
2
+d
3
)/2
mm
2
ultimate tensile strength R
m
MPa
yield strength R
p0.2
MPa
maximum tensile load F
0.2
= R
p0.2
x A
t
kN
ultimate tensile load F = Rm x A
t
kN
ultimate shear stress Τ
MPa
required shear area external thread A
th
=F/Τ
mm
2
Effective length of thread engagement L
e
1)
mm
1)
Minimum value of thread engagement length to make the tensile area determinative for the load at which the screw joint fails.
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