What is a Threadolet Fitting? Threadolet Dimensions

In the world of pipe fittings and connections, there are numerous options available to ensure the safe and efficient transport of fluids. One such option is the Threadolet. Threadolets are a versatile and widely used pipe fitting that plays a crucial role in various industries, including oil and gas, petrochemical, and manufacturing. In this comprehensive guide, we will delve into the world of Threadolets, exploring their design, applications, advantages, and installation procedures.

What is a Threadolet?

A Threadolet is a self-reinforced branch connection pipe fitting that allows for the connection of a smaller diameter pipe to a larger one. It features a threaded connection on one end and a welded connection on the other. Threadolets are designed to reduce stress concentrations and offer a smooth transition between the main pipe and the branch pipe, minimizing turbulence and pressure drop.

Threadolets are often used when connecting small-diameter pipes, instrument lines, or control lines to a larger pipe or vessel. They are particularly useful in applications where a strong, leak-free connection is essential. Threadolet pipe fittings are developed by the Company named Bonney Forge and because of that, they are also well known as Bonney Forge Threadolet. Fig. 1 provides an example of a threadolet.

Fig. 1: Threadolets

Types of Threadolets

Based on the pressure-temperature rating class there are two types of threadolets. They are:

  • Class 3000 threadolets, and
  • Class 6000 threadolets
READ  What is a Globe Valve? Working, Parts, Types

Threadolet Dimensions

Threadolet dimension basically means Outer and Inner diameter, Length of the hub, and thread dimensions. MSS-SP-97 provides the dimensional requirements for threadolet branch connections. Typical threadolet connections for each of the above-mentioned pipe classes are given below. Refer to these tables (Tables 1 and 2) along with the image in Fig. 2 below.

Threadolet Dimensions
Fig. 2: Threadolet Dimensions

Class 3000 Threadolet Dimensions

The dimensions of class 3000 threadolets are given in Table 1.

 Dimensions (Inches) Dimensions (mm) 
Outlet Size
in LB
in KG
3/813/161 1/43/40.20020.6431.7519.050.09
1/211 7/1615/160.25025.4035.7223.810.11
3/41 1/161 3/41 3/160.35026.9943.6629.370.16
11 5/162 1/81 7/160.60033.3450.8036.510.27
1 1/41 5/162 9/161 3/40.90033.3465.0944.450.41
1 1/21 3/82 7/162 11.00034.9372.2350.800.45
21 1/23 1/22 9/161.75038.1088.1165.090.79
2 1/21 13/164 1/1633.00046.04103.1976.201.36
324 13/163 11/164.35050.80122.2493.661.97
3 1/22 1/85 1/445.75053.98132.56101.602.61
42 1/464 3/47.10057.15151.61120.653.22
52 5/87 5/165 9/1612.00066.68185.74141.295.44
62 3/48 5/86 11/1615.30069.85219.08169.866.94
Table 1: Class 3000 Threadolet Dimensions

Class 6000 Threadolet Dimensions

The dimensions for class 6000 threadolet connections are provided in Table 2.

READ  Considerations for Storage Tanks Nozzles Orientation
 Dimensions (Inches) Dimensions (mm) 
Outlet Size
in LB
in KG
1/41 1/81 3/89/160.30028.5834.1314.290.14
3/81 1/81 3/89/160.30028.5834.1314.290.14
1/21 1/41 3/43/40.45031.7543.6619.050.20
3/41 7/16210.75036.5149.6125.400.34
11 9/162 7/161 5/161.25039.6961.9133.340.57
1 1/41 5/82 3/41 1/21.60041.2869.0638.100.73
1 1/21 11/163 1/41 15/161.95042.8682.5549.210.88
22 1/164 1/162 3/45.00055.03102.3969.852.27
Table 2: Class 6000 Threadolet Dimensions

Threadolet Materials

Threadolets, like other pipe fittings, are manufactured from a variety of materials to suit different applications. The choice of material depends on factors such as the type of fluid being transported, temperature and pressure conditions, corrosion resistance requirements, and specific industry standards. Below are some common materials used for Threadolets:

Threadolet MaterialMaterial Specification
Carbon SteelASTM A105
Staniless SteelASTM A182 Gr F-304, F-316, F-309, F-321, F-317
DSSASTM A182 Gr UNS-F44, F45, F51, F53, F55, F60, F61
Alloy SteelASTM A182 Gr F1, F5, F9, F11, F22, F91
Nickel AlloyUNS N10276, UNS 2200, UNS 2201, UNS 8020, UNS 6600, UNS 8825
Copper NickelASTM SB 61, 62, 151, 152
Table 3: Threadolet Materials

Applications of Threadolets

Threadolets find applications in a wide range of industries due to their versatility and ability to create strong, reliable connections. Some common applications include:

  • Oil and Gas Industry: Threadolets are extensively used in the oil and gas sector for connecting control lines, instrumentation, and small-diameter pipes to main pipelines and equipment.
  • Chemical and Petrochemical Industry: Threadolets are employed to connect auxiliary lines, such as sampling lines and vent lines, to process pipelines and vessels.
  • Power Plants: Threadolets are used in power generation plants to connect various instrumentation and control lines to the main steam and water lines.
  • Manufacturing Industry: Threadolets are utilized for connecting coolant lines and lubrication systems in manufacturing processes.
READ  PDMS Video Tutorial/Lessons for Beginners

Advantages of Threadolets

The popularity of Threadolets can be attributed to several key advantages:

  • Strength and Reliability: Threadolets create strong and leak-free connections, reducing the risk of pipe failures and leaks.
  • Versatility: Threadolets can be used in a wide range of applications and are available in various sizes and materials.
  • Reduced Stress Concentrations: The design of Threadolets helps distribute stress evenly, reducing the risk of stress-related failures.
  • Easy Installation: Threadolets are relatively easy to install, making them a cost-effective choice for many applications.

Installation of Threadolets

Installing Threadolets requires precision and expertise. Here are the basic steps involved:

  • Determine the appropriate location for the Threadolet on the main pipe.
  • Prepare the surface by cleaning and beveling the area where the Threadolet will be welded.
  • Weld the Threadolet onto the main pipe using the appropriate welding technique and filler material.
  • Connect the branch pipe to the threaded end of the Threadolet using a suitable thread sealant or tape.
  • Perform pressure testing and inspection to ensure the integrity of the connection.


Threadolets are a crucial component in the world of pipe fittings, enabling the safe and efficient connection of smaller pipes to larger ones in a wide range of industries. Their strength, reliability, and versatility make them a preferred choice for many applications. Understanding the different types, design considerations, and installation procedures of Threadolets is essential for ensuring their proper use and performance in various industrial settings.

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Posts