Page 1934 - Master Catalog 2017, Inch

Technical Information
Inch Screw Thread with UNJ Profi le

A thread system is available for aerospace and other applications where high fatigue strength is
required. The UNJ thread form is defi ned by ASME B1.15 and is similar to Military Specifi cation
MIL-S-8879. Screw thread assemblies consist of external and internal threads. In order to
minimize the stress on the external UNJ thread, a controlled root radius is required that
is equal to 0.15011P to 0.18042P, where P is the thread pitch. Internal UNJ threads are
not required to have a radius at either the major or minor diameters.

Nut:
UNx/UNJx

Screw:
UNx
UNJx

UNx:
R0.14434P-0.125P
Technical Information

Because external UNJ threads must be produced with a defi ned
B1.15. Please note this standard includes Class 3 and Class 2
root radius, standard UN tooling may not be used. However, For UNJ thread specifi cations, the reader is referred to ASME
internal UNF threads may be produced with ground thread UN UNJ screw threads. However, only Class 3 UNJ threads meet
taps sized to produce the proper class of fi t. The tap does not the requirements of Military Specifi cation MIL-S-8879. For
need to be marked with a letter J. Attention must be paid to the Unifi ed Inch (UN) thread specifi cations, refer to ASME B1.1.
tap drill since the minor diameter has to be specifi ed so as to
provide clearance with the root radius on the external thread.

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