Types of Threads: Definition and Thread Identifying

 

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.