Page 8 - THREADING CATALOG

INTRODUCTION ½ What Is a Thread?

Introduction

A lot of things around us, whether it be everyday objects
or industrial products, have a thread connection. The
A thread is a surface formed by a helical movement of
history of thread connections began many years ago.
a flat contour along a helical line. The basis of threading
is the principle of obtaining a helix. There are many
The first fastening parts with threads were used in ancient
Rome. However, due to the high cost, they were only used for
different standards, types and ways of producing threads.
jewelry, medical instruments and other expensive products.
stages of manufacturing the part, thereby occupying
Bolts and nuts were widely used in the 15th century. They
a responsible role for obtaining quality parts. The key
connected the mobile segments of armor and parts of
to high quality and efficient thread processing is a
watch mechanisms. The first printing machine, invented In many cases, the thread process occurs in the final
by Johannes Gutenberg between 1448 and 1450, had correct and well-composed technological process.
threaded connections - its parts were fastened with screws. The assigned thread machining strategy is directly related to
At the beginning of the 17th century, a threaded connection the correct selection of the cutting tool. It is the tool, a small
appeared similar to the type found today. Initially, the thread and seemingly minor element in the production of threads
pitch was only in inches until the French introduced the that can significantly increase productivity and quality.
metric thread only at the beginning of the 19th century. ISCAR understands the role of the tool, particularly in
At the present time, parts with threads are threading and metal processing in general, and
widely used in many different industries. aims to provide our customers with a reliable
tool that will meet their requirements.
Thread Parameters

Thread can be defined as a continuous helical ridge on the • Major Diameter – the largest diameter of two extreme
nut (inner part) or screw (outer part) of a cylinder. The ridge diameters. In external threads, the major diameter
is called a crest, and the dip or space between each crest defines the end limit of a thread profile and in internal
is referred to as the root. The side of the thread surface threads, the major diameter defines the start of a
that connects the crest and the root is called the flank. thread profile. Therefore, for external threads the
Screw (outer Part) Nut (inner Part) major diameter is an outer thread diameter and for
crest root crest root internal threads, the major diameter is an inner thread
diameter. Usually the major diameter of external
threads is smaller than the major diameter of internal
threads, if the threads are designed to fit together.
• 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
flank flank internal threads the minor diameter is an outer thread
diameter. Space between the minor diameter of an
Thread geometry with value, angles, radiuses, etc. contain external thread and the minor diameter of an internal
tolerances defined in thread standards. thread should be minimized to ensure correct thread
The main parameters of thread geometry and functionality, if the threads are designed to fit together.
thread functionality are: diameters, pitch, lead, • Pitch Diameter (Effective Diameter) – the pitch diameter
helix angle, lead angle, and truncation. is also known as an effective diameter, since this is
the most probable area for the external and internal
Diameters threads to engage. Pitch diameter is a theoretical
There are three main thread diameters: major diameter, diameter representing the place where the width of
pitch dimeter and minor diameter. Value and tolerances for the basic thread profile is equal to half a pitch.
each diameter differ according to each thread standard.
Screw (Outer Part) Nut (Inner Part)

minor diameter minor diameter
pitch diameter pitch diameter
major diameter major diameter

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