Page 9 - THREADING CATALOG

INTRODUCTION

Pitch / Threads Per Inch (TPI) When
Pitch and Thread per Inch (TPI) define the same φ = helix angle INTRODUCTION
threading feature, only in different terms. P = thread pitch
Pitch - a main and common parameter for all types of metric Dpitch = pitch diameter (effective diameter of thread)
threads, usually expressed in millimeters. Pitch defines π ≈ 3.142
the distance along a line parallel to the axis of the thread
length between the sides of the thread profile placed in φ
the same axial plane on one side of the axis of rotation. P
Pitch for Metric Threads
pitch πxD

Thread per Inch (TPI) - a main and common parameter φ 3
for all types of inch-based threads. TPI defines the P φ 2 φ 1
count / number of threads per distance of 1 inch
along the length of threads placed in the same πxD3
axial plane on one side of the axis of rotation. πxD2
Theads Per Inch (TPI) πxD1
1” Lead Angle
Lead angle is the angle between the helix of thread
and a plane of rotation. The lead angle of the thread
depends on the pitch diameter, thread pitch, and
Lead the number of thread starts. This parameter can
Lead is the distance that defines an axial movement be represented as a sweep of a right triangle.
of any point moving in relative motion per one full The angle of the thread is calculated
turn (360°) along a line parallel to the thread axis. In by the formula given below:
a single-start thread, the lead is equal to the thread Lead

pitch. In a multi-start thread, the lead is equal to the φ = arctan ( )
L
thread pitch multiplied by the number of starts. π×Dpitch
Single-Start Double-Start Triple-Start Lead= n×P
lead lead lead
pitch pitch pitch When
φ L = lead angle
Dpitch = pitch diameter (effective diameter of thread)
P = thread pitch
N = number of thread starts
π ≈ 3.142
Where the thread is single-start, the lead
angle is equal to the helix angle.

Truncation
lead=pitch lead=2xpitch lead=3xpitch
Truncation is the perpendicular distance to the
axis of the thread from the imaginary point of
Helix Angle intersection of two adjacent sides of the thread
profile to the nearest point of its top or bottom.
The Helix Angle of the Thread Influences Thread Efficiency and
Is Necessary for Calculating Torque in Thread Applications. truncation
The Helix Angle of the Thread Can Be Defined by Unraveling
the Helix from the Thread, Representing the Section As a truncation
Right Triangle and Calculating the Angle That Is Formed.

P
φ= arctan ( π×Dpitch )

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