Effective length of thread engagement
 External thread fastener:
 Thread - steel grade -
 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 At =π/4 d02 ; d0=(d2+d3)/2 mm2
 ultimate tensile strength Rm  MPa
 yield strength Rp0.2 MPa
 maximum tensile load F0.2 = Rp0.2 x At kN
 ultimate tensile load F = Rm x At kN
 ultimate shear stress Τ MPa
 required shear area external thread Ath=F/Τ mm2
 Effective length of thread engagement Le1) 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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