Types of Threads: Definition and Thread Identifying
Definition
of thread
Types of
Threads: Definition, Parts and Thread Identification Tools :-
Threads play a very important role in engineering lines especially for making various items of daily life. Machines are used almost every moment in the manufacturing industry and almost all machines are incomplete without threads. Technically speaking, spiral grooves of equal measurement or size made in circular cylindrical articles or pipes are called threads or in other words, spiral grooves of equal pitch and equal depth formed on parallel circular cylindrical surfaces or conical circular surfaces are referred to as threads.
Thread is
the main part
Generally the three main parts of the thread are as follows:
* Shank diameter
*Threads Per Inch (TPI)
* Correct
1. Shank
diameter
The diameter of the shank is represented by the diameter of
the thread as the number increases as the diameter of the thread. Shank size
will determine which screw thread is most compatible or ideal for a particular
job.
2. Threads
Per Inch (TPI)
It is usually abbreviated as TPI. This is the number of
threads available or designed in one inch (1"). Lower TPI choices of 7 and
8 represent coarser screws while 18 or 22 provide finer screw threads for metal
fasteners.
3. Point
The most common types of screw points are self-piercing
points and self-drilling points.
Self
piercing point:- It has sharp point designed to cut material like
screw thread.
Self
Drilling or Drilling Point:- It is equipped with a drilling
feature at the tip of the screw which is used to make a hole through the metal
before fastening the threaded pieces together.
How to identify different types of threads?
Before you begin, make sure you have two thread detection
tools on hand;
1. Pitch
gauge
A pitch gauge refers to a device used to measure the distance
between the crests of a thread. The number of threads per inch is measured for
NPT, UN/UNF, BSPP and BSPP. If the observer has a metric thread, the pitch
gauge will mark the distance between each individual crest in millimeters.
A caliper refers to the device used to measure the diameter
of a thread. For male threads, it only measures the outer diameter whereas for
female threads it measures the inner diameter. For all advanced users, there is
a digital caliper available in the market that saves time and simplifies the
process.
There are different types of threads, so it is important to
know all types of threads along with their characteristics and applications so
that a correct type can be selected by the user while using these instruments.
Scroll down to know more about thread types.
Parallel threads are threads that contain:
*UN/UNF
* BSPP
*Metric parallelism
Tapered
threads are threads that include:
*NPT/NPTF
* BSPT
*Metric Tapered
The diameter of the thread can be looked at to identify whether the thread is tapered or parallel. If the diameter of the thread is found to be thinner towards the end, it is confirmed that it is a tapered thread. Where the thread diameter is found to be the same at the top and bottom of the thread, it can be termed as parallel thread.
There is another way by which you can find out whether it is
a parallel thread or a tapered thread, if the threads touch the entire length
of the caliper then it is definitely a parallel thread otherwise it is a taper
thread.
A device known as a thread pitch gauge tool should be used to
determine the thread size. Thread pitch gauge helps you accurately measure and
calculate the number of threads within a required distance.
One should have two methods when it comes to determining the
actual size of the thread. Before starting one must determine if your thread is
a pipe thread (NPT/NPTF, BSPT, BSPP) or not (UN/UNF, Metric Parallel, Metric
Tapered). One must note that the tapered thread can be a pipe thread. If you
have pipe threads available you can compare the thread size to a nominal size
profile.
If you are working for non-pipe threads (UN/UNF, metric
parallel, metric tapered) you must use a caliper tool to measure the outside
diameter of the thread.
4)
Designated thread
These steps involve a designated thread as per industry
standards for further use. Start by identifying the thread size and then note
the type and pitch.
13 different
types of threads
When it comes to thread types most of the people who work in
the industry recognize the thread types as they are used in almost all types of
industries. Mainly threads and connections are divided into six types which are
as follows:
*UN/UNF
*NPT/NPTF
*BSPP (BSP, Parallel)
*BSPT (BSP, Tapered)
*Metric parallelism
*Metric Tapered
There are
13 different types of threads which are as follows:
*Left hand thread
*Right hand thread
* Taper thread
*"V" shaped thread
*Metric or international thread
*British Standard Thread
*Vendor thread
* Square thread
* Acme thread
*Buttress thread
*Worm thread
* Knuckle thread
*Single and multi-threaded
1. Left
hand thread
Left-handed threads are referred to as threads that lean
towards the left hand. These are fixed in motion against the forks. For
example, the thread on a screw with a left-handed thread, which is so cut that
the bolt, screw, or nut has to be tightened by turning it counter-clockwise.
This type of thread is rarely used.
2. Right
Hand Thread
Right-handed threads are referred to as threads that lean to
the right. They are fixed in clockwise motion which is also called right hand
thread.
3. Taper
Thread
Taper thread is the thread found cut around the taper surface
and thus named as taper thread. This thread can be right hand or left hand.
Uses of taper threads are as follows:
To join two or more machine parts such as nuts-bolts and
studs.
To get mechanical levers for lifting weights like chain
pulleys, jacks etc.
For high accuracy in precision instruments like micrometers.
For power transfer jobs.
To control or reduce speed.
4. V-Shape
Thread
V-shape thread is the type of thread that is available in the
shape of the English alphabet V. These types of threads are most commonly used
and can be cut or manufactured by tap, die, lathe, milling etc. Threads are
available made up of different standards.
5. Metric
or International Thread
Metric or international thread is the type of thread
originally adopted in central France from 1898 to 1908. As usage grew, all
other international countries also started using it. However, the Indian
Standards Institute has also taken up this thread so far.
These threads are made at an angle of 60°. This type of screw
is available in flat and basic round. As per I.S 1330-1958, the number of
threads is 20 per inch and its pitch is 2.5 mm.
6. British
Standard Thread
a) British
Standard Whitworth Threads
British Standard Whitworth threads are the type of thread
that originated in Great Britain and named after Sir Joseph Whitworth who was a
famous citizen of Great Britain who invented this thread in 1841.
This is the thread that was used to provide the convenience
of interchangeability and is used in common nut-bolts and various other
applications. The angle of these threads is 55° and its crest with roots is
rounded. These threads are also called B.S.W. thread.
b) British
Standard Fine Thread
British Standard Fine Thread is the thread which is very
similar in shape to B.S.W. Thread This thread angle is also same as BSW thread
i.e. 55°, where the number of threads per inch is higher which means less thread
thickness. This in turn is responsible for strengthening the grip. Nut bolts
with this type of thread are used where there is high vibration.
c) British
Association Threads
British association thread is a type of thread used in small
or miniature electrical and mechanical devices such as radios, televisions,
electrical products, meters and clocks. This type of thread angle is 471/2°
which can easily be used for 1/2″ or 6mm nut bolts.
d) British
Standard Pipe Thread
British Standard pipe threads are available with a 55° angle
cut at 3/4 taper per foot. This type of thread is used in sanitary pipe
fittings, steam pipes, gas pipelines as it does not leak due to taper.
7. Vendor
Thread
Seller thread is the type of thread known as American
national thread. They are recognized by the American Standards Institute and
are a type of V-shaped thread. These threads have an angle of 60° and also have
flat roots and crests. The same standards institute was responsible for
inventing the national fine thread which is a very thin thread. These are
threads that are used in most motor vehicles as well as airplanes.
8. Square
thread
Square threads are referred to as threads that have a very
strong root. It is named as it appears to form a square, and these threads are
used for lifting heavy loads, transferring power, applying pressure, and
machining screw jacks and vice spindles. There is no fixed measurement or
number per inch of such threads.
9. Acme
Thread
Acme threads are referred to as threads that are more or less
similar to square threads in that their shape is flat at the bottom and thin at
the top. Compared to square threads, they are easier to cut on a job and are
considered stronger. These threads have diagonal ends and hence it is easy to
fix or loosen the split nut but it has no reaction. Acme threads are made at a
29° angle.
10. Buttress
Thread
Buttress threads are referred to as screw threads which have
a triangular cross section but have one face at right angles to the axis of the
screw and the second face is simply inclined. These threads have higher tensile
strength than square threads. This is the only reason these are used in cases
where extra tension is required on one side and which must be absorbed.
11. Worm
thread
Worm threads are referred to as threads which are found to be
almost identical to Acme threads whereas Acme threads are found to be deeper.
Worm thread angles are available at 29° and are so named as they are used in
motor vehicle worm wheels to transfer power at 90° angles. As the three teeth
of the worm wheel engage the shaft with the worm thread, they are properly
installed.
12. Knuckle
thread
Knuckle threads are referred to as threads which are quite
strong and coarse in nature and used in heavy and light work. These are threads
that are found in semi-circular form on both the root and crest sides. These
threads can also be cast into a mold.
13. Single
and Multi-Thread
Considering a particular piece of work, it is possible to
have different types of threads associated with it. Therefore, there are
single-threaded screws and multiple or multi-start threaded screws which are
important and highly used in various applications. Independent threads are also
termed as starts which include single-start, two-start, three-start etc.
As soon as a turn is completed, the screw or bolt is rounded
then a thread is a movement where the screw is referred to as a single threaded
screw and once multiple threads are a movement, the screw can be referred to as
a multiple or multi-start threaded screw.
Now considering the case of a three-start thread, in one complete turn, the thread advances three times more than if it were treated as a single thread. Multi-start threads are referred to as those that are used in areas where springs require rapid movement or speed. These are the areas that are widely used.
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