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
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.
Read also: Screw Thread Terminology
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 at 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
#1 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.
#2 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.
#3 Taper Threads
In this type, the threads are cut on the tapered surface called taper threads. These are used 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 micrometers.
- In jobs of power transfer.
- To control or reduce speed.
#4 “V” Shape Threads
This type of thread is in the shape of the English alphabet “V”. It is most widely used. These types of threads can be cut or made by tap, die, lathe machine and milling, etc. These threads are made of different standards.
#5 Metric or International Threads
These types of threads were initially adopted from 1898 to 1908 in central France. Over 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 before 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)
#1 British Standard Whitworth Threads
These types of threads 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)
#2 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.
#3 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 recognized through numbers, which range from 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
#4 British Standard Pipe Threads
Its angle is 55°, which is cut at 3/4 taper per foot. It is used in sanitary pipe fittings, steam pipes, and gas pipelines. Because of the taper, it does not leak.
#6 Seller Threads
These threads are known by the name American national thread. It has been recognized 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 airplanes etc.
Thread Angle = 60°
Depth of thread = 0.649519 X Pitch
Dia = 0.866025 X Pitch
Crest = D/ 8
Root = 0.125 X Pitch
#7 Square Threads
This thread has a very powerful root. Its makeup is square. These threads are used for lifting heavy loads, transfer of power, exerting 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
#8 Acme Threads
These threads are more or less like square threads, but their shape is in taper i.e., flat from the 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 a 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″
#9 Buttress Threads
It is a screw thread that 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
#10 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 the coupling of rail coaches.
#11 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 wheels of motor vehicles to transfer power at 90°. As three teeth of the 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.
#12 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 screws and multiple or multi-start threaded screws. 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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Closing It Up
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