Page 10 - Threading

INTRODUCTION • Minor Diameter – the smallest diameter of two extreme diameters. In external threads,
the minor diameter defines the start of a thread profile and in internal threads, the
minor diameter defines the end limit of a thread profile. Therefore, for external threads
the minor diameter is an inner thread diameter and for internal threads the minor
diameter is an outer thread diameter. Space between the minor diameter of an
external thread and the minor diameter of an internal thread should be minimized to
ensure correct thread functionality, if the threads are designed to fit together.
• Pitch Diameter (Effective Diameter) – the pitch diameter is also known as an
effective diameter, since this is the most probable area for the external and internal
threads to engage. Pitch diameter is a theoretical diameter representing the
place where the width of the basic thread profile is equal to half a pitch.

Pitch / Threads per Inch (TPI)
Pitch and Thread per Inch (TPI) define the same threading feature, only in different terms.

Pitch - a main and common parameter for all types of metric threads, usually expressed in
millimeters. Pitch defines the distance along a line parallel to the axis of the thread length
between the sides of the thread profile placed in the same axial plane on one side of the
axis of rotation.
Pitch for Metric Threads

pitch

Thread per Inch (TPI) - a main and common parameter for all types of inch-based threads. TPI
defines the count / number of threads per distance of 1 inch along the length of threads placed
in the same axial plane on one side of the axis of rotation.

Theads per Inch (TPI)

1”

8 ISCAR