PROPER USE AND CARE OF RING GAGES
Ring Gages
Thread ring gages have a great responsibility in any Quality Control facility that inspects threaded products. They can make the primary decision as to whether the thread falls within maximum and minimum functional size limits resulting in an acceptance or rejection of a product’s thread. The correct results depend on two key points: The accuracy of the gages and the proper use and care of the gages.
Pitch Diameter
The product’s size limits are expressed in terms of pitch diameter. Limit type gages check the functional size of the threads. This takes into consideration not only the pitch diameter, but also the effects of deviations in other factors such as lead, angle, roundness, helical path, etc. Functional size relates to the capability of the product to assemble with mating parts and the degree of tightness or looseness of the fit. Borderline-sized parts are unavoidable and decisions regarding this matter depend on the accuracy and correct use of the gages.
Accuracy of The Gages
The accuracy of the gages is the responsibility of the gage manufacturer. If the manufacturer is reliable, they will produce the gages well within the allowable tolerances. To maintain the accuracy becomes the responsibility of the user. Mishandling of the gages, such as dropping them can knock them out of calibration. If this should occur, the inspector would need to check the gage or gages on the matching setting plug to evaluate their accuracy. Damage or premature wear results in unnecessarily high costs, not only for replacement gage or gages, but also, more importantly, for rejected products.
GO Gage
The GO gage must enter or be entered by the product’s thread without undue force or pressure. Common sense along with proper instructions are important and must be used with care. The gage must travel over the full length of the threads for the product to be accepted. If you feel that the threaded product is entering the Go gage with some resistance, then refer to ASTM F788/788M for the maximum allowable torque you can use for acceptance of the product.
NOT GO Gage
The NOT GO gage has a limitation on entry. It is usually preferable that it does not enter. However, to be realistic, some entry is generally acceptable. ANSI/ASME B1.2 1983 section 5.2.1 allows up to three turns in the NOT GO gage. In cases of exceptionally thin or ductile material or small number of threads, it may necessitate modification of this practice. You will need at least 1-2 fully formed threads on the threaded fastener to stop in the NOT GO gage. Without 1-2 full formed threads, the threaded fastener may not stop due to insufficient thread height and width associated with the lead threads.
Several Suggestions Regarding Use & Care of Ring Gages:
- Clean the parts before gaging of foreign material.
- Keep the gages clean and lightly oiled.
- Align the starting threads carefully with the gage so as not to cross thread which can damage the end threads of both the product and gage.
- Don’t force the gage. Use light pressure only.
- Protect the gage from damage such as nicks or rust and store properly.
- Use thread ring gages equally, by using both sides of the gage. They are made to be used from either face and will prolong the wear life.