13 Types of Threads & How They Work [Complete Guide] Images

On: April 26, 2021

In this post, you’ll learn what are the different types of threads or forms of threads in the manufacturing nuts and bolts. Download the PDF file at the end of this article.

Threads and Its Types

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Thread plays a very important role in the engineering line for manufacturing various items of daily use. In this engineering and scientific age, machines are used every moment at every stage. Without threads, most of the machines cannot be used.

Definition of Threads

Spiral grooves of equal measurement or shapes made on a round cylindrical article or pipe are known as threads. In other words, spiral grooves of equal pitch and equal depth made on the parallel round cylindrical surface or conical round surface are called threads.

For example, if we take a round stick and wind a piece of wire in angular indication, the wires twist would move ahead on the round stick. The path on which the wire moves ahead is called Helix. Like this helix, the thread is inclined in an angle on a round surface. Threads may be internal or external.

As already mentioned above, the shape or size of threads depends upon their utility. Thread cutting tools are also made accordingly. According to their shapes.

Types of Threads

Following are the 13 different types of threads:

Right-hand threads
Left-hand threads
taper threads
“V” shape threads
Metric or International Threads
British Standard Threads
Seller Threads
Square Threads
Acme Threads
buttress Threads
Knuckle Threads
Worm Threads
Single and Multi-Threads

Right Hand Threads

These threads are inclined towards the right-hand side. These are tightened in a clockwise movement. These are known as right-hand threads.

Left Hand Threads

These threads are inclined towards the left hand. These are tightened in anticlockwise movement. For example, on a screw with left-hand threads, threads are so cut that the bolt, screw, or nut has to be turned in a counter-clockwise motion to engage or tighten it. Their use is comparatively less.

Taper Threads

Threads cut on around but taper surface is called taper threads. These are sued for shafts like buffing spindles. These threads can be right hand or left hand.

The above threads are used for the following purpose:

To join two parts of a machine like nut-bolt and stud.
To get mechanical livers for lifting weights, such as chain pulleys, jacks etc.
For accuracy in precision instruments like micrometres.
In jobs of power transfer.
To control or reduce speed.

“V” Shape Threads

This type of threads is in the shape of the English alphabet “V”. It is most widely used. This types of threads can be cut or made by tap, die, lathe machine and milling etc. These threads are made of different standards. The following types are mostly used.

Metric or International Threads

This types of the thread were originally adopted in 1898 to 1908 in central France. With the passage of time, other international countries also started using it. The Indian standards institute has also adopted this thread.

These threads are made on jobs of 0°25 mm to 300 mm in diameter. Its angle is at 60°. Its screw is flat and the root is round. According to I.S. 1330-1958, these are written prior to the letter M and figure written after “M” indicates pitch such as -M20 X 2.5. It means the number of threads is 20 per inch and its pitch is 2.5 mm.

Thread Angle = 60°

Crest and root = 0. 125 X pitch

Pitch =1/T.P.I. ( in mm)

British Standard Whitworth Threads

This type of threads is originated from great Britain. sir joseph Whitworth, a citizen of Great Britain invented this thread in 1841. This thread was to provide the facility of interchangeability. It is used in ordinary nut-bolts and other jobs. Its angle is 55°. Its crest, as well as root, are in round shape. It’s known as B.S.W. Thread.

Thread angle= 55 °

Pitch = 1/T.P.I

Depth = Pitch X 0.6403

Radius = Pitch X 0.1373

Core dia = D- (1.28 X Pitch)

(D= outer dia of bolt)

British Standard Fine Thread

In shape, this thread is similar to B.S.W. thread. The angle of this thread is also 55° but the number of thread per inch is more i.e the thickness of threads is less. This makes the grip more strong. Nut bolts having this thread are used where is more vibration.

British Association Threads

This type of thread is of every think make-up. It is used in small and tiny electrical and mechanical instruments like radio, television, electrical goods, meters and watches. The angle of these threads is 47 1/2°. These can be used for 1/2″ or 6 mm nut bolts.

These are recoghinsed through numbers, which range between 0 to 12. number 0 = 0. 236″ or 6 mm. Number 12 = 0.0511″ or 1.3 mm.

Thread Angle = 47 1/2″

Depth of thread = 0.6 X Pitch

Pitch = 1/T.P.I

D = 1.36 X Pitch

British Standard Pipe Threads

Its angle is at 55° which cut at 3/4 taper per foot. It is used in sanitary pipe fittings, steam pipes, gas pipelines. Because of taper, it does not leak.

Seller Threads

These threads are known by the name of American national thread. IT has been recognised by the American standards institute. It is a “V” shape thread. Its angle is at 60°. ITs roots and crest are flat. The same standard Insititute has invented national fine thread, This thread is thin. IT is used in motor vehicles and aeroplanes etc.

Thread Angle = 60°

Depth of thread = 0.649519 X Pitch

Dia = 0.866025 X Pitch

Crest = D/ 8

Root = 0.125 X Pitch

Square Threads

This thread has a very powerful root. ITs make up is square. These threads are used for lifting heavy loads, transfer of power, to exert pressure, screw jack, lead screw of machines, press machines and vice spindle instruments. Their specific measurement and number per inch are not fixed.

Thread Angle = 90°

Depth of Thread = 0.5 X Pitch

Crest and Root = 0.5 X 5

Acme Threads

These threads are more or less like square threads but their shape is in taper i.e. flat from bottom and thin from the top. It is comparatively easier to cut it on a job than the square threads. IT is also considered stronger. AS these threads have slanting ends, it is easier to fix or unscrew the split nut on it. There is no backlash in it. This thread is made at 29° angle.

Thread Angle = 29°

Depth of Thread = 0.5 X Pitch + .01″

Crest = 0.3707 X Pitch

Root = 0.33707 X Pitch – 0.0052″

Buttress Threads

It is a screw thread which is triangular in section but which has one face at right angles to the axis of the screw, the second face only being sloped. IT has more pulling power than square thread. This is why it is used in cases where the excessive pull is on one side and it must be absorbed as in a ratchet.

Root and crest = 0.125 X Pitch

Thread Angle = 45°

Depth = 0.75 X Pitch

Knuckle Threads

This thread is also very strong. It is used in heavy and light jobs of rough nature. This is half round at both root and crest. It can be cast in a mold.

Depth of Thread= 0.5 X Pitch

Root and crest Radius = 0.25 X Pitch

These threads are specially used for coupling of rali-coaches.

Worm Threads

Their shape is almost similar to Acme Threads but these are deeper than Acme threads. Their angle is also at 29 °. This thread is used in worm wheel of motor vehicles for the transfer of power at 90°. As three teeth of worm wheel fit into the shaft with worm threads, they fit well.

Thread Angle = 29°

Depth of Thread = 0.6866 X Pitch

Root = 0.32 X Pitch

Crest = 0.335 X Pitch.

Single and Multi-Threads

In a piece of work, it is possible to have some separate and independent threads running along with it. Thus, there are a single-threaded screw and multiple or multi-start threaded screw. The independent threads are called starts, and we may have single-start, two-start, three-start, etc.

For one complete turn round the screw or bolt then there is a movement of one thread the screw is called a single-threaded screw. And when there is a movement of more than one thread, the screw is called multiple or multi-start threaded screws.

In the case of a three-start thread, for one complete turn, the thread advances three times as far if it were a single thread. Multi-start threads are used in those cases where fast movement or motion is needed Fountain where they are widely used.

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