# The Types And Geometric Parameters Of Screw Threads

A thread or a screw thread is a bridge covering the cone and cylinder. It is the main feature in thread fasteners and screw machines and is vital in converting between linear and rotary motions. It is present in the helix form, crucial for its conversion.

## Geometric Parameters Of The Screws Threads

### Outer Diameter (Major thread diameter)

The outer diameter is also recognized as the external or major thread diameter. It is the diameter of the non-existent cylindrical surface coinciding with the crest of the thread. It is considered the thread’s largest diameter and the screw diameter.

The height of the helix is lifted in the upward direction and around the outer thread. The measurement of the outer diameter can be done using a clipper. In addition to clippers, you can also use a thread pitch gauge for its accurate measurement.

Clippers are commonly used to take male thread measurements. In contrast, you can use a thread pitch device to measure a female thread. Measuring both threads with appropriate tools can help in saving both money and time.

### Inner Diameter (Minor thread diameter)

The inner diameter is also designated as a minor thread diameter. The diameter of the non-existent cylinder coincides with the thread’s bottom. The inner diameter helps measure the thread root at the intersection area. Moreover, you can also measure the thread base by measuring the inner or minor thread diameter.

Similar to the outer diameter, you need special equipment to measure the inner diameter of the thread. For example, you can use a floating carriage micrometer to measure it. The micrometer has a fixed spindle on one side of this floating carriage micrometer. The other side possesses a micrometer with a moveable spindle, helping to accurately measure the thread’s inner diameter.

### Pitch Diameter (Effective diameter)

Another name for this diameter is an effective diameter, and you can calculate it by imagining a cylinder. The cylinder diameter must exit where the thread crest and groove width are equal. They should be equivalent to half the nominal thread pitch and equal to one another. It is the diameter of a non-existent coaxial cylinder utilized for intercepting the thread’s surface.

### Pitch

It is also known as thread pitch. It is the total distance between the screw thread and its threshold. It is the distance between a point and its threshold. It should be on the equal screw thread. You can measure the axis to the pitch of the thread in a parallel manner. The pitch of the thread is also measured using special equipment. A thread gauge or a screw gauge is commonly used to measure the thread’s pitch.

It is the axial distance covered by the thread of the screw in a single turn. Lead and pitch are comparable in single-threaded screws. In the case of double-threaded screws, the lead should be doubled the pitch. If there is a triple-headed screw, the lead should be thrice than the pitch.

### Tooth Angles

The geometry and shape of the thread are referred to as tooth angle. The tooth angles vary greatly in shape. It can be in triangular, square, or trapezoidal form, and the reason that you can get the threads in different styles and shapes.

The side angles of the thread that is measured axially are known as the threaded angles. It is also referred to as the angles of the thread.

## 13 Different Types Of Screw Threads And Their Use

Screws Threads are divided into different types. Its main types are explained below.

Knuckle threads are also referred to as round threads. As the name suggested, they are present in round form. They are present in the half-rounded form at the crust and root. Both crust and root possess large rounded spaces between them. This space uses for shifting debris to prevent the thread from any damage due to the debris particles. These threads have high strength and are moldable.

• You can use it for rail coaches’ coupling.
• Being debris-resistant, it offers applications in oilfields.
• It is used in automobiles for “low eye” in European countries.

Acme threads are considered alternatives to square threads because they share similarities. They have tapered shapes with slanting ends, i.e., a thin top and a flat bottom. Because of the slanting end, you can easily fix split minutes on them. In addition, they are designed at an angle of 29°. They are known to exhibit greater strength.

• It shows wide applications in C.N.C. systems.
• You can use it for lead screws and jack screws.
• It is used in industrial applications that need power transmission.
• It is also used on an industrial scale for those applications requiring heavy torque.

Another identification of the seller thread is the American national thread. The reason behind this is their recognition by the American standard institute. The thread has a 60° angle and a V-shape. It usually possesses a flattened crest and root.

• You can use it on tapped holes and nuts.
• It can effectively be used on screws and bolts.

From 1898 to 1908, Central France first used the international or metric thread. Later, many other countries started taking advantage of this thread. It designs in such a way that it has rounded roots and flat screws. Its diameter ranges from 0°25 mm to 300 mm and has an angle of 60°.

Uses of International or Metric Threads:

• You can use it on tapped holes and nuts.
• It can effectively be used on screws and bolts.

Tapered threads generally have a tapered design. Whenever the thread’s flank is compressed against one another, the female and the male end of the threads automatically form a seal due to its tapered design. These threads can be left-hand threads or right-hand threads.

• It can be used for forming outstanding seals.
• Tapered thread can be used in shafts such as buffing spindles.
• You can use it to reduce or control the speed.
• It may be used for joining two components of machines,
• For making outstanding seals, it is a good choice.
• This type of thread is ideally used in power transfer jobs.

Buttress thread is a screw thread having a triangular section. It possesses two faces, one of which is sloped while the other one is at the right angle to the screw axis. This thread’s pulling power is much greater than the square thread. Moreover, their strength is similar to the strength offered by the V-threads.

• You can use a buttress thread to transfer power in a single direction.
• It is used as a lead screw in heavy loads machines.

Square threads are designed in a square shape. The root of this type of thread is very strong. But it has less strength than the V-threads. It doesn’t have a fixed number per inch or any other measurements. It is known to have greater efficiency. The pitch of this thread is two times more than the B.S.W. thread.

• You can use it to transmission power.
• Square thread can use to exert pressure.
• You can use it in press machines.
• It is good to use in the vice spindle instruments.

Sir Joseph Whitworth invented the British Standard Whitworth thread in 1841, which is the reason behind the name of this thread. It is an asymmetrically designed V-shaped thread having an angle of 55° between its flanks. It has a round-shaped root and crest.

Uses of British Standard Whitworth Thread:

• It is specifically used in components such as screwed fastenings and bolts.
• British standard Whitworth thread is widely used in nut bolts and can be used for the adjustments of lines.
• It is used in those conditions where a large amount of strength is needed at the roots.

The shape of this thread looks like the “V” letter. You can use different machines for the manufacturing of this type of thread. These may include milling machines, lathe machines, and die or tap. Various standards are used for the manufacturing of this thread. It has a flank angle of 60°. It is considered the most widely used thread among all threads.

• V-shaped threads are commonly used in fasteners and bolts.

In some conditions, a single workpiece may possess different independent and separate threads known as starts. You can say that the workpieces are single-threaded and multiple-threaded screws. Single-threaded has a single thread or a single strat. On the other hand, multiple threads consist of multiple threads or multiple starts.

Uses of Single and Multiple Threads:

• It is used in those conditions which require fast motion.
• You can use single-start for fastening purposes.
• Multiple starts can be used for the transmission of power.

Left-hand threads are also called reverse threads, inclined in the direction of the left hand. They are tightened while moving in an anti-clockwise direction. Left-handed threads run in a counterclockwise direction. They offer fewer applications.

• It is used in various automotive components, such as bolts of tires.
• Left-hand thread is commonly used in gas-supply valves to differentiate them from oxygen-controlling valves.
• You can use it for fitting the pipes.

Right-handed threads are the opposites of left-handed threads. These threads are inclined in the direction of the right hand. They are tightened during their movement in a clockwise direction.

• It is commonly used in components such as nuts and bolts.
• You can also use this thread type in pipe fittings.
• It is also widely used in screws.