Maximizing Drill String Integrity: A Guide to FH Rotary Shouldered Connection Gages

In the oil and gas industry, the reliability and integrity of drilling equipment are paramount. Among the critical components ensuring these qualities are the FH (Full Hole) rotary shouldered connection thread plug and ring gages. These tools are essential for verifying the dimensions and quality of threads on rotary shouldered connections, ensuring they meet the stringent standards required for safe and efficient drilling operations. This article explores the significance, specifications, and applications of these gages, highlighting their role in maintaining industry standards and enhancing operational performance.

What is an FH Rotary Shouldered Connection?

FH, or Full Hole, refers to a specific type of rotary shouldered connection widely used in the petroleum and natural gas industries. These connections are threaded joints that link various components of the drill string, such as drill pipes, drill collars, and subs. The design of FH connections enables them to withstand high torque, compression loads, and tension during drilling operations.

Key Features of FH Connections:

  1. Thread Form and Profile:

    • FH connections feature a tapered thread form with a V-shaped profile, typically either V-040 or V-050, depending on the nominal size and pitch.
    • The thread form angle is 60 degrees with a taper of 1:16.
    • Thread height is 0.8 times the pitch, with flat thread crests and roots.
  2. Thread Length and Bore Diameter:

    • FH connections have a longer thread length compared to other rotary shouldered connections like NC or REG, providing a larger contact area between the pin and the box.
    • This design enhances joint strength and fatigue resistance.
    • The larger bore diameter facilitates smoother flow of drilling fluids, reducing the risk of clogging.

Role of Thread Plug and Ring Gages

Thread plug and ring gages are precision tools used to measure the dimensions and quality of threads on FH rotary shouldered connections. These gages ensure the threads comply with the specifications and standards set by the American Petroleum Institute (API), particularly API Spec 7-2, which is the latest edition covering rotary shouldered connections, including FH connections.

Measuring and Verification Process:

  1. Dimensional Accuracy:

    • Thread plug gages measure the internal thread dimensions of the connection, ensuring they are within specified tolerances.
    • Thread ring gages verify the external thread dimensions of the connection.
    • These measurements include critical aspects like lead, taper, height, flank angle, and profile.
  2. Compliance with API Standards:

    • API Spec 7-2 outlines the dimensional requirements, gauging practices, and gauge specifications for FH connections.
    • The inspection results from the gages are compared against the acceptance criteria and tolerances specified in the standard.
    • This compliance is crucial for ensuring the reliability and safety of the connections in demanding drilling environments.

Applications and Benefits

FH connections, verified by thread plug and ring gages, are widely used in the drilling industry due to their high performance, reliability, and durability. They are particularly suitable for deep and directional drilling, as well as for operations in harsh environments. Key benefits include:

  1. High Axial and Bending Load Resistance:

    • FH connections can withstand significant axial and bending loads, making them ideal for complex drilling operations.
  2. Pressure and Temperature Resilience:

    • These connections are designed to perform under high pressures and temperatures, essential for deep-sea and high-temperature drilling conditions.
  3. Excellent Sealing and Corrosion Resistance:

    • The design of FH connections ensures a robust seal, reducing the risk of leaks.
    • Materials used in FH connections are often chosen for their corrosion resistance, extending the lifespan of the equipment.
  4. Enhanced Fluid Flow:

    • The larger bore diameter of FH connections facilitates better fluid flow, improving drilling efficiency and reducing operational issues related to fluid clogging.


The use of FH rotary shouldered connection thread plug and ring gages is integral to maintaining the standards and efficiency of drilling operations in the oil and gas industry. These gages ensure that the critical components of the drill string meet stringent API specifications, thus enhancing the reliability, safety, and performance of drilling equipment. For industry professionals, understanding and utilizing these gages correctly is crucial for achieving optimal drilling outcomes and maintaining operational integrity.

For technical assistance and more information, you can contact our team of experienced engineers at Westport Corp, who have over a century of combined experience in API gaging. We are here to assist with any questions or special requirements you may have. Reach us at 888-400-4243 or email your prints to quote@westportcorp.com.


1. What is an FH rotary shouldered connection?

  • An FH rotary shouldered connection is a type of threaded joint used in the oil and gas industry to connect various components of the drill string. It is designed to withstand high torque, compression, and tension during drilling operations.

2. Why are thread plug and ring gages important for FH connections?

  • These gages are essential for measuring the dimensions and quality of threads on FH connections, ensuring they meet API specifications. This verification is crucial for the reliability and safety of drilling operations.

3. What are the benefits of using FH connections in drilling operations?

  • FH connections offer high axial and bending load resistance, pressure and temperature resilience, excellent sealing and corrosion resistance, and enhanced fluid flow, making them ideal for deep and directional drilling in harsh environments.

4. How can I ensure my FH connections meet API standards?

  • Using thread plug and ring gages to measure and verify the threads against API Spec 7-2 standards is essential. Regular inspections and compliance checks help maintain the quality and performance of FH connections.

For further inquiries or technical support, please contact our experienced team at Westport Corp.

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