Related Resources: calculators
Length of Screw Thread Engagement Calculator and Table
Fastener, Bolt and Screw Design Torque and Force Calculations
ISO Hardware Engineering Data
ANSI Hardware Engineering Data
Length of Screw Thread Engagement per. ISO 9651 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 · d^{0.2}
Eq. 2
Normal LE max. = 6.7 · P · d^{0.2}
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, 
Pitch P mm 
Length of Engagement Normal LE Rounded 

Rounded to nearest mm 
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 B1.13M2005 (Revision of the ASME B1.13M2001)
Related
 Thread engagment rules of thumb vs. published standards
 Screw Stress Area 100 ksi & Greater
 Bolt Stress Area less Than 100 ksi
 Bolt Elongation Equation and Calculator while under Axial Stress
 Fastener / Thread Tensile Area of External Thread Formula
 Fastener / Threaded Pitch Circle Diameter Formula and Calculation
 Fastener / Threaded Shear Area Formula and Calculation
 Bolt Fastener Preload Torsion Load Stress Formulas and Calculator per. MILHDBH60
 Bolt Elongation by Turn Formulas and Calculator per. MILHDBH60
 Bolt Preload Tension Equation and Calculator
 Bolt Preload Tension Force Calculator
 Torque vs Tension Bolts Table Chart SAE J429 Bolts