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### Length of Screw Thread Engagement Calculator and Table

Length of Screw Thread Engagement per. ISO 965-1 Calculator, Formula and Table

Length of engagement of mating threads is selected to utilize full tensile strength of a bolt prior to shearing nut threads. Other applications may require internal thread shear prior to failure of theoretically threaded part

For the calculation of the limits of the normal length of thread engagement in Table 1,

the following formulas have been used and their values rounded.

For each pitch, P, within a certain diameter range, d has been set equal to the smallest diameter within the table range.

Eq. 1
Normal LE min. = 2.24 · P · d0.2

Eq. 2
Normal LE max. = 6.7 · P · d0.2

Eq. 3
Threads per mm = 1 / P

Where

d = Basic Major Diameter, mm
P = Pitch distance single thread, mm

The length of screw thread engagement given below (Table 1), have been calculated from formulas and then rounded off to the nearest values in the R40 series of preferred numbers in accordance with ISO 3 for the three decimal places required. If a fourth decimal place results, it is further rounded.

Table 1 Length of Screw Thread Engagement Tabulated

 Basic Major Diameter, d Over - up to and including mm Pitch P mm Length of Engagement Normal LE Rounded Rounded to nearest mm (Less than is considered short) Rounded to nearest mm (More than is considered long) 1.5 - 2.8 0.2 0.5 1.5 0.25 0.6 1.9 0.35 0.8 2.6 0.4 1 3 0.45 1.3 3.8 2.8 - 5.6 0.35 1 3 0.5 1.5 4.5 0.6 1.7 5 0.7 2 6 0.75 2.2 6.7 0.8 2.5 7.5 5.6 - 11.2 0.75 2.4 7.1 1 3 9 1.25 4 12 1.5 5 15 11.2 - 22.4 1 3.8 11 1.25 4.5 13 1.5 5.6 16 1.75 6 18 2 8 24 2.5 10 30 22.4 - 45 1 4 12 1.5 6.3 19 2 8.5 25 3 12 36 3.5 15 45 4 18 53 4.5 21 63 45 - 90 1.5 7.5 22 2 9.5 28 3 15 45 4 19 56 5 24 71 5.5 28 85 6 32 95 90 - 180 2 12 36 3 18 53 4 24 71 6 36 106 8 45 132 180 - 355 3 20 60 4 26 80 6 40 118 8 50 150

References

American Society of Mechanical Engineers Standard ASME B1.13M-2005 (Revision of the ASME B1.13M-2001)

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