Selecting the most economical and suitable thread types makes your task easy and reliable. Therefore, identification of cotton threads, polyester threads and Royan threads is essential for connecting accessories. Straight threads (also called parallel threads) and tapered threads are the two main types of threads.
There are different types of topics. The main types include parallel threads, including BSPP, UN/UNF, and metric parallel threads. The second type of thread is tapered threads, including metric tapered threads, BSPT threads and NPT threads/NPTF threads.
What is a screw thread?
We use a spiral structure to convert between rotary and linear motion, called a thread or screw thread. Screw threads are essential features of a screwdriver and threaded fasteners.
We can use screw threads in various applications. It is a ridge rolled into a cone or cylinder. The screw thread is shaped like a helix. The pitch of a screw thread is the linear distance the screw can travel in one revolution, and the mechanical advantage of screw threads depends on their pitch.
There are two common thread shapes: straight threads and tapered threads.
Straight threads have a parallel profile whose diameter remains the same throughout the part.
Tapered threads taper along with the thread profile and their diameter decreases towards the bottom.
Thread geometric parameters
Before we present the types of threads, let's have an overview of the most important geometric parameters of the thread.
1) Outer diameter (main thread diameter)
The external and internal diameters are geometric parameters of a thread. The outside diameter (OD) is the largest material diameter of a gear or threaded feature. External or external thread diameter refers to the diameter of a screw and includes a high spiral height around the thread. You can use a tape measure or thread pitch gauge to measure the outside diameter.
The outer diameter or outer diameter is measured with a screw with an external thread.
The outside diameter of an internal thread (or inside diameter) can be measured using a thread cutter. The outer diameter of the external thread is calculated using a tap. A thread pitch gauge allows you to measure internal and external threads with a tap to save time and money.
2) Inner diameter (small thread diameter)
The core diameter can be defined as an imaginary cylinder that can contact the thread roots (a protruding part of the thread) of an internal thread or the thread roots of an external thread.
Special equipment is required to measure outside and inside diameters. The inside diameter is the diameter of a screw, which can be measured at the root of the thread, the intersection of the screw, or the base of the thread.
3) Part diameter (effective diameter)
The effective or partial diameter is the diameter of an imaginary coaxial cylinder that can cut the thread surface. The diameter of the part can intersect such that the point of intersection in a cylinder generator is at the point where the diameter of the part meets the opposite flanks of the thread groove. The thread groove corresponds to half the nominal thread pitch of the screw.
You can use a thread pitch gauge to check and determine the thread diameter and size. Thread pitch gauge can be helpful to accurately calculate and measure thread number within a certain distance. You can try different measuring devices for this purpose.
4) Argument
Thread pitch or thread pitch is the distance from a point on the same screw thread to a corresponding limit.
The thread pitch is on the closest thread that can be measured parallel to the shaft. Must be between corresponding points on an adjacent surface in the same axial plane.
5) Lead
We can define pitch – the distance a screw thread can travel axially in one revolution. The pitch and pitch are equal on a single start screw, while the pitch on a double start screw is twice the pitch. For a three-entry screw, the pitch is three times larger.
6) Tooth Angle
Tooth angle refers to the shape and geometry of a thread. Wires come in different shapes and designs. The tooth angle can be trapezoidal, square or triangular.
7) Thread angle
The angle formed between the flanks of the thread, measured in the axial plane, is called the thread angle or thread angle.
Different types of screw threads
There are different types of topics. The main types include parallel threads, including BSPP, UN/UNF, and metric parallel threads. The second type of thread is tapered threads, including metric tapered threads, BSPT threads and NPT threads/NPTF threads.
1) Metric thread or international thread
Metric threads or international threads were the first international standards, and we use metric threads throughout the world for general screw threads. The “M” in metric threads indicates the nominal outer diameter of the screw thread.
“M” on a metric thread also indicates the diameter of the smooth-wall hole. The ISO metric thread is a universal thread and a fine thread has a smaller pitch compared to a coarse thread.
2) British Standard Topics
The British Standard Whitworth (BSW) thread was developed and specified by Joseph Whitworth. It is a thread standard based on imperial units and was the world's first national standard for tapered pipe threads.
British Standard threads are one of the main thread types and have coarse pitches and are based on many other standards such as BSCon, BSF and BSCopper. BST is used for special purposes such as line configuration and can be found on pins.
BSF (British Standard Fine Pitch Thread) increases vibration during automotive and aircraft manufacturing work and thread adjustment. These types of threads can also be used for the internal and external thread size of iron and steel pipes where high strength is required. The thread form of BST is as follows:
1. British Standard Pipe Parallel Thread (BSPP)
2. British Standard Taper Thread Pipe (BSPT)
| BSP thread size | Outer diameter mm/inch | ICC |
| 1/16 inch BSP | 7.7mm / 0.304″ | 28 |
| 1/8 inch BSP | 9.7mm / 0.383″ | 28 |
| 1/4 inch BSP | 13.16mm / 0.518″ | 19 |
| 3/8 inch BSP | 16.66mm / 0.656″ | 19 |
| 1/2 inch BSP | 20.99mm / 0.825 inches | 14 |
| 5/8 inch BSP | 22.99mm / 0.902″ | 14 |
| 3/4 inch BSP | 26.44mm / 1.041″ | 14 |
| 7/8 inch BSP | 30.20mm / 1.189″ | 14 |
| 1 inch BSP | 33.25mm / 1.309″ | 11 |
| 1-1/4 inch BSP | 41.91mm / 1,650″ | 11 |
| 1-1/2 inch BSP | 47.80mm / 1.882″ | 11 |
| 2 inch BSP | 59.61mm / 2.347″ | 11 |
| 2-1/4 inch BSP | 65.71mm / 2.587″ | 11 |
| 2-1/2 in. BSP | 75.18mm / 2.96″ | 11 |
| 3 inch BSP | 87.88mm / 3.46″ | 11 |
| 4 inch BSP | 113.03mm / 4.45″ | 11 |
| 5 inch BSP | 138.43mm/5.45 inches | 11 |
| 6 inch BSP | 163.83mm / 6.45″ | 11 |
3) Uniform Thread Standard (UTS)
Unified Threads Standard is one of several types of threads with rounded ends and roots. Unified threads consist of three classes:
1. This type of thread is used for applications that require large tolerances for easy assembly.
2. This class of unified threads is often used for general applications.
3. The final class of unified standard threads is used where precision of threaded elements and fit are absolutely necessary or important.
Unified Threads Standard (UTS) is the main standard thread type for nuts and bolts and has the same 60° profile as ISO metric thread.
The Unified Thread Standard is the only thread format used in three countries, namely Canada, the United States and the United Kingdom, under an agreement with the included angle of 60° to allow easy exchange of thread identification machines and tools. The uniform thread standard is a general purpose thread controlled by ANSI/ASME in the USA.
4) “V” shaped threads
V-shaped threads are common and can be cut with a lathe, tap or die. The thread shape is similar to the English alphabet “V”, as its name reflects the shape of the screw threads.
5) Square strands
The square thread is highly efficient. It is used for power transmission and in high load applications such as jacks and spindles. The square thread is a common thread shape among the various thread types and is named after the square cross-section of the thread.
The square thread consists of the most efficient thread shapes, but it is not easy to manufacture. The square thread has the lowest friction and is widely used due to its high efficiency. Square thread types can be found in tools, spindles, machine tool feed mechanisms, and helical gears.
The square thread is less stable than the V thread, but offers less resistance to friction during movement than the Whitworth thread.
6) Acme Wire
Acme thread is mainly used for brass valves, lathes and threading machines. It is a modification of the square thread and can be easily manufactured. Acme thread is more stable compared to square thread. There are three types of general-purpose Acme threads: 2G, 3G, and 4G. Each class is used for assemblies and clearances in all standard diameters.
7) Ankle wire
Round thread is a thread form from screw thread terminology and can be used for rough and rough work. It has a rounded top and bottom. It is delicate and prone to damage and dirt easily. The round thread is a modification of the square thread and can be easily cast and curled. The round thread angle is 30 degrees. Round threads are one of several types of threads used in glass bottle necks, coupling gears, valves, fittings, gate valves, fire hydrants, large molded insulators for the electrical industry, and railway car couplings.
8) Reinforcement wires
Buttress threads are also known as two-entry profiles:
1. Buttress thread: type of lead screw used in machines, known as locking thread. This allows the thread to support large loads in one direction. It has low friction.
2. Sawtooth pipe thread is a kind of trapezoidal tapered pipe thread used in the petroleum industry as a hydraulic seal thread.
Buttress threads have the advantages of V and square threads and are used to transmit power in one direction. They have the same strength as most V-threads and the low frictional resistance of square threads.
The buttress thread engagement height is 0.6p and has a clearance angle from the normal to the axis of 45 degrees. Common examples of sawtooth nuts and rods include aircraft propeller hubs, large weapon locking assemblies, and columns for hydraulic presses.
9) Worm threads
Worm threads are one of the different types of threads similar to trapezoidal threads as their shape is also 29 degrees. One difference is that they are deeper than trapezoidal wires. We use worm threads in automobile worm wheels. It can be transmitted at 90 degrees because when using a worm gear shaft, three teeth of the worm wheel fit into the shaft. They can work well.
10) Single and multiple threads
In screw thread terminology, there are also some independent and separate threads that can work with a workpiece. Therefore, single-start screws and multi-start threaded screws are used for some workpieces.
1: Single start screw refers to the screw, when you turn the screw or screw completely, it is called single start screw. It is also called a star and can be unidirectional, bidirectional or triple.
2: A multi-thread screw is a moment with more than one thread. We can use multi-start threads when movement or fast movement is required.
Important tips for choosing the right thread
To choose the right thread you need to pay special attention to some thread-specific properties. It guarantees adequate resistance and better performance for various applications. Some of these tips are listed below.
● Not all thread types are suitable for all applications. Each type is designed specifically for its specific task and is made from different materials to perform different functions.
● Some screw threads may require sharp designs for direct drilling, while others may require pre-drilled holes to function properly.
● Thread spacing may vary for other screws, which is very important for different screw thread properties.
University Degree
The product design takes into account the use of different types of yarn. In addition to processing threads directly onto parts, there are also methods for helicoil and copper inserts. Different types of threads and thread processing methods are used for products made of different materials, and professional quality control tests are carried out.
