Thread Ring Gages | By: Carlis Stuber

Thread Ring Gages

A frequently asked question in our "Hands-On" Gage Calibration and Repair workshops:

Q: How do I correctly set my thread plug gages?

A: The answer lies in the interpretation of the standard. The following information was
gathered using guidance from the H-28 Handbook, Machinery's Handbook and
various Manufacturers literature.

The United States accepted standard for setting thread ring gages is to "set" or "fit" the thread ring gage using a thread setting plug. Refer to the H-28 Handbook for more information. (There are other methods but according to the H-28 handbook this is the accepted method.) The requirement for setting the thread ring gage to a thread plug gage is stated in various terms depending on which reference you follow. The standard may read "set the ring gage to a minimum drag" or "set the ring gage to a noticeable drag" or "fit the thread ring gage to the thread set plug". This is of course a very subjective test based on the standard. It is best to order a thread setting plug at the same time you order a thread ring gage. This will allow the manufacturer to "match" the items and will give you a reference in case a gage is dropped or abused. When sending these gages to the calibration laboratory send both the ring and plug gages for calibration. Refer to the H-28 Handbook for more information. Here is a technique learned from a Gage manufacturer. It may help you in the process of setting your ring gages.

Adjusting Thread Ring Gages

1.	Thoroughly Clean both the thread ring and plug gages
2.	Lightly lubricate the setting plug gage
3.	Turn the locking screw of the ring counter-clockwise until it is loosened, but do not remove it from the ring
4.	Turn the adjusting screw clockwise to open the ring to a larger pitch diameter than the setting plug
5.	Gently turn the ring gage onto the setting plug until it completely engages with at least one thread of the ring extending beyond the last thread on the back end of the full-form (larger diameter) setting plug.
6.	Turn the adjusting screw counter-clockwise until there is a slight drag between the ring and setting plug
7.	Turn the locking screw until it is tight. There should now be a "noticeable (minimum) drag" between the ring and the setting plug
8.	Repeat this process until the "noticeable (minimum) drag" desired is achieved Gently unscrew the ring from the plug.
9.	Again, Gently turn the ring gage onto the setting plug until it completely engages with at least one thread of the ring extending beyond the last thread on the back end of the full-form setting plug.
10.	Again, Gently turn the ring gage onto the setting plug until it completely engages with at least one thread of the ring extending beyond the last thread on the back end of the full-form setting plug.
11.	There should be a "noticeable (minimum) drag" on the ring gage as you turn it onto the thread ring.
12.	While the ring gage is at the larger diameter of the setting plug try to move it from side to side to test for a bellmouth condition*
13.	Remove the ring gage from the setting plug. As you remove the ring gage you should notice the same "noticeable (minimum) drag" throughout the gage length.
14.	Turn the ring gage 180° and insert the thread setting plug from the opposite direction.
15.	The ring should exhibit the same "noticeable (minimum) drag" that you felt from the other direction for the entire length of the ring gage. (You may feel a slightly tighter drag on the larger diameter of the setting plug due to more contact.) Repeat steps 12-13
16.	When the gage is properly set there should be a uniform feeling over the entire length of the plug with no end play. (There may be some play if the plug and the ring were not ordered and manufactured as a mating set.)

*If you encounter a "bellmouth" condition contact your gage distributor or manufacturer for possible rework.

Carlis Stuber
Q.C.S. - Executive Director

About the Author
Doug Stohr Carlis graduated from Chippewa Valley Technical College in the Quality Technician program, received honorary mention from Metro State University for work in Quality Management with emphasis in Calibration and Calibration Systems, Graduated from World Missions School of Ministry with a Pastoral and Teaching emphasis.

Carlis completed A2LA Training at A2LA.

Carlis has nearly 30 years of Quality experience dealing with automotive and agricultural manufacturing. His experience includes Quality Management, Quality Engineering, Inspection, Sales, Calibration and Calibration Training, Teaching and Consulting.

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