Calibration Procedures for Thread Ring Gages

1. Examine the ring for evidence of rust, corrosion, nicks or burrs and note the condition of seals. Remove rust and/or burrs. If the rust or corrosion is too extensive to be removed or if nicks or burrs are still present which will interfere with proper setting of the ring, reject the ring and proceed no further.
2. Ensure that the set plug is clean, inspect it for nicks or damage, and verify that it is within tolerance. Lubricate the set plug with a thin film of light oil. Depending on the size, it may be advisable to clamp the handle of the setting plug in a vise.
3. To determine the “as received” condition measure the minor diameter and record the reading. If possible, screw the set plug into the ring without using excessive force, to assess condition of the thread in the ring per steps 6 through 9.
4. When necessary, remove the sealing wax and turn the locking screw counter-clockwise until it is loose. Turn the adjusting screw clockwise, which opens up the ring, until the set plug enters freely. In some cases, a small screwdriver may need to be levered into the adjustment slot to facilitate the opening of the ring as you turn the adjusting screw.
5. Turn the ring all the way on to the full form section of the truncated setting plug. Turn the adjusting screw counter-clockwise until there is a slight drag between the set plug and ring. Turn the locking screw clockwise until it is tight and rotate the ring to assure the proper fit. After adjusting, and with the set plug still inserted, tap the ring with a soft-tipped hammer to properly seat the threads. If the degree of drag changes after tapping, the ring was not properly seated. Repeat the setting procedure. This operation may have to be repeated more than once to obtain and maintain the proper degree of drag. The degree of drag is somewhat subjective. The degree of drag for a small ring should be less than that for a large ring but in no case, should the ring spin freely nor should it be so tight as to cause unnecessary wear or damage to the set plug.
6. Once set correctly on the full form, turn the ring across the truncated portion of the set plug. There should be only a slight change or no change of fit from the full-form portion to the truncated portion. A satisfactory fit on both the full-form and truncated portions of the set plug, indicates, with a high degree of probability, that the pitch diameter, flank angles and lead of the ring are within tolerances. If the ring becomes significantly looser on the truncated portion it should be reworked or replaced. Some may find it easier to reverse the procedure and turn the ring on to the set plug until the truncated portion of the set plug is fully engaged. Make the adjustments for proper fit as above. Once properly set to the truncated portion turn the ring across the full-form portion. Again, there should be no significant change in the degree of drag. If the ring will not go across the full-form portion the ring should be reworked or replaced. Do not attempt to force the ring across the full form portion of the set plug as damage to the crest of the set plug may occur.
7. If using a progressive set plug, screw the ring on to the front (Section 1) portion of the set plug and set as in steps 4 and 5. Once properly set, turn the ring to the back (Section 2) portion of the set plug. Section 2 of the set plug should not enter the ring more than 1.5 turns. If the ring goes over the max portion more than 1.5 turns, it should be reworked or replaced.
8. Remove the set plug from the ring and insert the set plug into the other side of the ring. The fit should remain consistent with the fit felt on the original side to assure proper straightness.
   
   Note: Although not a common occurrence, due to the specified +/- tolerances applied to the flank angles of both the ring and the setting plug, it is possible that once a ring gage is properly set on one side, the “feel” may not be the same when screwing the ring on to the setting plug from the opposite side. If this happens, it could be due to variations in the flank angles of the plug and ring that do not align with each other in both directions.
   
   Example:
   
   If the lead flank on the set plug is close to the “plus” limit, and the trailing flank is close to the “minus” limit, and the ring has one flank that is close to the “plus” limit and one flank that is close to the “minus” limit, the ring, when set to the set plug in the direction where the “plus” and “minus” flanks align with each other, may not go onto the set plug when reversed. Conversely, if the ring is set on the side where the “plus” and “minus” flanks do not align with each other, it may feel loose when reversed.
   
   If this situation occurs, and measurements show that the flank angles are within their tolerances on both the setting plug and ring gage, and the mismatch in their alignment is the reason for the difference in fit from opposite sides, the following procedures shall be followed:
   
   In order for a GO ring to correctly perform its function of passing over the full threaded length of the product (see section 5.1.1), and for it to be able to perform this function from both sides of the ring, the ring shall be set to the side with the tighter fit and the setting shall be deemed to be acceptable.
   
   In order for a NOT GO ring to correctly perform its function of not passing over the product thread more than three turns (see section 5.2.1), and for it to be able to perform this function from both sides of the ring, the ring shall be set to the side with the looser fit and the setting shall be deemed to be acceptable.
   
   
9. To check for bell mouth, or taper, insert the set plug up to 2 turns into the ring and note if there is any shake or play. Shake or play indicates a bell mouth or tapered condition and the ring may need to be reworked or replaced.
   
   Note: When evaluating an adjustable thread ring using a calibrated set plug other than the set plug to which the ring was originally manufactured, the fit will not necessarily be the same due to allowable differences in the functional size of different set plugs. If the threads in the ring are still within acceptable limits, it will be possible to correctly reset the ring to the new/different set plug. After correctly resetting the ring, the minor diameter may end up out of tolerance. If after being properly reset the minor diameter is oversize, it is most likely due to differences in the functional size of the set plugs, but if the minor diameter is undersize, it could be due to differences in functional size of the set plugs or due to wear on the flanks of the ring. In either case the minor diameter must be in tolerance for the ring to be considered acceptable.