Page 7 - Threading_Handbook

• 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 INTRODUCTION
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”

7