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# Threaded Bolts - Stress Area

## Threaded bolts tensile stress area.

The weakest points in a bolt is the stressed area in the thread root. The stressed area depends on the type of threads - coarse threads reduces the stressed area compared to fine threads.

### UN and UNR Bolts Tensile Stress Area

The stressed area in a bolt can be calculated as

A = (π / 4)  (dn - 0.9743/ n)2                                      (1)

where

A = stressed area (in2)

dn = nominal bolt diameter (in)

n = 1 / p = number of threads per inch

p = pitch, length per thread (in)

Despite that a reduced area will reduce the breaking load of a bolt - coarse threads are used for clamping. Fine threads bolts are weaker due to the reduced thread height.

### ISO 898 Bolts Tensile Stress Area

Tensile stress area in bolts according ISO 898-1 Mechanical properties of fasteners made of carbon steel and alloy steel:

As,nom = (π / 4) ((d2 + d3)/ 2)2                        (2)

where

As,nom = nominal stress area (m, mm2)

d2 = the basic pitch diameter of the external thread according ISO 724 ISO general-purpose metric screw threads -- Basic dimensions (m, mm)

d3 = d1 - H / 6 = the minor diameter of external tread (m, mm)

d1 = the basic minor diameter of external thread according ISO 724

H = the height of the fundamental triangle of the thread according ISO 68-1 ISO general purpose screw threads (m, mm)

## Related Topics

• Miscellaneous - Engineering related topics like Beaufort Wind Scale, CE-marking, drawing standards and more.
• Fasteners - Bolts, nuts and threaded rods - torque, tension and loads.

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