API Gaging - Thread Ring and Plug Gages for Oil and Gas

American Petroleum Institute (API) Gages

API working plug and API thread ring gages are manufactured to American Petroleum Institute (A.P.I) specifications and are used as the benchmark for calibration by the National Institute of Standards and Technology (NIST). The manufacturing process for our API plug and ring gages are licensed by the American Petroleum Institute (API) to Spec Q1, Spec 5B, Spec 7 & Spec 11B.

As an ISO 17025 accredited and ISO 9001 registered company we are always working to raise the bar in order to provide you with the highest quality products. Our API plug and ring gages are produced with only the highest quality tool steel hardened to Rockwell C60-63. Our special heat treat and cold treat process insures maximum gage stability. Each API plug and ring gage is then precision lapped to provide superior accuracy, optimum gage surface finish and longer wear life for the gage. Finally, they are inspected and certified in our state-of-the-art environmentally controlled laboratory insuring your API plug and ring gages provide unmatched quality, accuracy, stability, reliability and durability.

Our team of engineers has served on many different API gaging subcommittees with over 100 years of experience. We are here to assist you with any questions or special requirements you may have.

Please contact us at: 888-400-4243 with any questions or quoting you require or email your prints to quote@westportcorp.com

API gages are available in:

Casing - Round

Sucker Rods P1-P8 & B1-B6

American National Special Thread

Line Pipe

Sucker Rods P2-P8 & B2-B6

Full Hole

Tubing-Non Upset

Polished Sucker Rods

Internal Flush

Tubing-External Upset

Extreme Line Gages


Tubing-Integral Joint

Negative Flank Angle

Slim Hole

Extreme Line Casing


Extra Hole

NC connections


Wide Open

Regular Rotary Shoulder Connections

D1-22, D1-42




Tapered Thread Gages-AWWA

Special custom gage designs


Spec 5B (API Plug and Ring)

Normal Size
Specifications / Applications From To TPI TPF
Casing – Round 4 1/2 13 3/8 8 3/4
Line Pipe 1/8 13 3/8 8-27 3/4
Tubing - Non Upset 1.050 3 1/2 10 3/4
4 4 1/2 8 3/4
Tubing - External Upset 1.050 1.900 10 3/4
2 3/8 4 1/2 8 3/4
Tubing - Integral Joint 2 3/8 4 1/2 10 3/4
Extreme Line Casing 5 7 5/8 6 1 1/2
8 5/8 10 3/4 8 1 1/4



Spec 7 (API Plug and Ring)

Normal Size
Specifications / Applications From To TPI TPF
NC Connections NC 10 NC 16 6 1 1/2
NC 23 NC 50 4 2
NC 56 NC 77 4 3
Regular Rotary Shoulder Connections 1 8 5/8 14-6 1 1/2, 2, 3
Full Hole 3 1/2 6 5/8 4-5 2, 3
Internal Flush 2 3/8 5 1/2 2 2

Oil Field Related Connections (API Plug and Ring)

Normal Size
Specifications / Applications From To TPI TPF
H-90 2 3/8 8 5/8 3-3 1/2 1 1/4, 2, 3
Slim Hole 2 3/8 4 2
Extra Hole 2 7/8 5 4 2
Wide Open 2 3/8 4 2
AOH 2 3/8 4 1/2 4 1 1/2
PAC 2 3/8 3 1/2 4 1 1/2
XHole 2 7/8 3 1/2 4 2



Spec 11B

Normal Size
Specifications / Applications From To TPI
Sucker Rods P2-P8 & B2-B6 1/2 1 1/8 10
Sucker Rods P1-P8 & B1-B6 1/2 1 1/8 10


Who is the American Petroleum Institute and how to choose the right 

API Plug Gage and API Ring Gages

The American Petroleum Institute (API) is a trade association for the oil and natural gas industry. The institute works with governments and other legal and regulatory associations to negotiate standards and perform research. About 400 companies are represented by the API, all involved with some part of the petroleum industry. The API also creates and certifies industry standards. The standards are published for all manufacturers involved in the petroleum industry. The specifications are very comprehensive; they are intended to improve health and safety, comply with legislation, protect the environment, and boost efficiency. Each technical standard covers a specific area of production, refinement, distribution, or manufacturing of equipment used. API standards are recognized and used by the National Institute of Standard and Technology.

WESTport Corporation’s provides API plug and ring gages to industry that are compliant and/or licensed to Spec Q1, Spec 5B, Spec 7 and Spec 11B. The descriptions of each specification can be found below.

Spec Q1

The API Spec Q1 is not associated with any specific equipment. Instead, it relates to the quality of the manufacturing process and the company’s quality management system. A quality management system focuses on meeting customer and industry expectations of quality. The quality management system concerns the organizational structure, processes and resources. Another widely used quality management standard is ISO 9001, and WESTport Corporation is an ISO 9001 registered company as well.

Spec 5B

This Specification concerns API Master thread gages and their dimensions and marking requirements. It also covers other instruments and methods for inspecting threads. Specific products covered by this standard include:

  • Round casing
  • Line pipe
  • Tubing—Non Upset
  • Tubing—External Upset
  • Tubing—Integral Joint
  • Extreme Line Casing

Spec 7

The API Spec 7 covers all the requirements for drill-stem members. It includes specifications for Master gages, threaded connections, and gaging practice. While it largely deals with valves, specifically kelly valves, it also covers the following plug and ring gages:

  • NC Connections
  • Regular Rotary Shoulder Connections
  • Full Hole
  • Internal Flush

Spec 11B

The API Spec 11B contains the requirements and guidelines for steel sucker rods and other rods, and other related parts. It does not cover guides, rotators, shear tools, on-off tools, stabilizer bars, or guidelines for installation or maintenance. WESTport Corporation offers

  • Sucker Rods P2-P8 & B2-B6
  • Sucker Rods P1-P8 & B1-B6

Written by K. Hansen, Edited by Robert Forbes – WESTport Corporation – March 2, 2015