Thread Ring Gages

Thread Ring Gages also referred to as thread ring gauges are used to check the outside major diameter and pitch diameter limits on threaded parts. Thread Ring gages are available in ACME , Straight Pipe and Taperpipe styles.


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  • Thread Ring gages are AGD – American Gage Design
  • Precision hand lapped to provide optimum finish and superior accuracy
  • Manufactured to the highest end of the ANSI specifications to provide maximum wearability
  • Final inspection of thread ring gauges is completed in an environmentally controlled ISO 17025 laboratory
  • Free NIST certificate of accuracy with all thread ring gages

WESTport Gage provides a comprehensive line of Thread Ring Gages to meet all of your gaging needs. Click on any of the links above for a detailed product description along with pricing. For your convenience you can order online, email us at info@westportcorp.com with any technical questions or call us at 800-876-8587 and one of our friendly team members will gladly assist you.

ACME Thread Ring Gages: ACME Threads are used for translation motion in machine tools like lead screws where rapid movement is required or in screw jacks, where load to be shared is more. WESTport Gage provides a complete line of standard and special General Purpose ACME GO/NO GO Thread Ring Gages in compliance with ASME B1.5 - 1997. Acme Thread Ring Gages are used to gage an external threaded product. There are three classes of fit for ACME General Purpose thread gages; 2G, 3G and 4G.

Taperpipe Thread Ring Gages: NPT THREADS are used in general purpose application of pipe assembly, where a pressure tight joint of pipes is made, by making the pipes wrench tight using a sealing compound. NPT L1 taper pipe ring gages are used to check external threaded parts. NPT L1 rings inspect the functional size or hand tight engagement of the pipe, nipple or male threads. NPTF L1 ring gages are used to check external threaded parts. NPTF L1 ring gages inspect the functional size or hand tight engagement of the pipe, nipple or male threads.  NPTF gages are used to inspect pipe threads that are used in Dryseal applications NPTF (Dryseal) NPTF 6 step ring gages check the crest truncation or profile of the external threads and are used in conjunction or relationship with the L1 ring.

Straight Pipe Thread Ring Gages: Straight pipe thread ring gages are manufactured per ANSI/ASME B1.20.1. The threads are designed for free fitting mechanical joints. Straight pipe thread gages include NPSM, NPSF, NPSC, NPSL, NPSI, NPSH, and NH sizes.

Thread Ring Gages: Thread ring gages are adjustable and used to measure threads on an outside diameter (OD) to ensure the threads are within its designed tolerance limits. They are manufactured to an X tolerance and American Gage Design standards (AGD). Available in GO or NOGO, Class 2A or 3A for inch and to X Tolerance, Class 6g for metric.

ANPT Thread Ring Gages: WESTport provides a complete range of Aeronautical National Form Taper Pipe Thread Ring Gages per SAE AS71051. ANPT thread ring gages are intended for use on pipe, rings, fittings, and similar devices in aeronautical components and equipment requiring a sealed thread joint and where straight threads and gaskets or O‐rings are inadequate.

Pg Conduit Thread Ring Gages: Checks threads of pipe fittings used for electrical wiring. Pg Steel Conduit Thread Ring Gages are manufactured per DIN 40431 and inspect conduit threads.

Miniature Thread Ring Gages: Unified Miniature Screw thread ring gages are intended for use in watches, instruments, and miniature mechanisms. They provide a full range of Unified Miniature Screw Thread Ring Gages per the American Standard B1.10M 2004 and the equivalent ISO Recommendation.

Thread ring gages: are used to check and calibrate the threads on an external diameter. Like many other thread gages, these gages use a GO and NO GO method to determine if the threads fall within the tolerance or the class of fit. Thread ring gages are quite simple to use; if the GO end screws on, and the NO GO end will not screw on past three complete turns, then the part is within tolerance. WESTport Corporation offers thread ring gages in classes of fit 2A and 3A for inch gages and are made to an X Tolerance. The class of fit 2A is used for parts that do not require high precision, like standard bolts used for appliances and similar products. Class 3A is used for very precise machine parts and high quality products. Unified Series thread ring gages are available in UNC, UNF, UNEF and specials. Metric gages are offered in X tolerance and Class 6G.

All thread ring gages are precise calibration instruments, so it’s important never to force the gage onto a part, as this could alter the gage and destroy its integrity. For proper maintenance; store gages individually after dipping them in a rust preventive to prevent oxidation of the metal. If a gage is dropped or nicked, it may lose its ability to measure to the specification it was manufactured to.

Thread ring gages are manufactured are available as solid thread ring gages or more commonly as an adjustable thread ring style. Solid rings are very dimensionally accurate as they measure the pitch diameter and minor diameter. The solid design also means that if they are dropped, they are less likely to need re-calibration assuming the threads have not been damaged.

Adjustable style thread ring gages have a slot in the ring that allows the user to calibrate the gages to a setting plug. The setting plug determines if the gage is within tolerance and fully accurate. The ability to tune the gage to a setting plug lowers production costs and increases the life of the gage. When the gage needs to be recalibrated, it can be sent back to the manufacturer for adjustment and certification in an ISO 17025 accredited laboratory.

The standardization of thread ring gages is governed by ASME/ANSI B1.2. All of WESTport Corporation’s thread ring gages are manufactured to the highest end of these specifications, and they are inspected in an environmentally controlled ISO 17025 laboratory.

Written by K. Hansen, Edited by Robert Forbes – WESTport Corporation – July 29, 2016