API thread gage calibration is a vital component of confirming pitch diameters and streamlining master gages for use. When calibrating an API thread gage, pitch sizes should match accommodating ring gages—complimenting calibrated and clean set plugs. Such cleaned surfaces provide the following important benefits:

  • Non-nicked surfaces
  • Tolerant to applied pressure
  • Correct tapering
  • Proper lubrication

API Thread Gage Cleaning and Inspection

Before calibration occurs, API thread gages should be inspected for embedded fillings, nicks, and burrs. Any impurities should be removed, and sealing wax may be lifted via a knife. The gage may be prepared through turning its locking screw in a counter-clockwise direction—and should be loosened completely.

Once the adjusting screw has been turned completely, the ring gage may be turned, with its setting plug pushed back, to reveal a single thread beyond the setting plug. This creates uniform wear, and it prolongs the thread gage’s lifespan.

API Thread Gage Setting

Once the thread gage’s ring has been set, it may be tapped with a small hammer to confirm solidarity. Re-checking the gage’s drag is important during calibration, as unchanged drag keeps a gage properly set, and it increases its usefulness.

The ring gage may be turned from full-form sections to truncated sections within the set plug’s front area. The created drag will be similar, and it will reduce shakiness within the ring. Once looseness is removed, the flank angles and root relief will be protected from wear and tear. If tolerance decreases—or, if setting the thread gage proves increasingly difficult—the gage must be removed and completely replaced.

API Thread Gage Engagement

The set plug should be removed from the rung, and the ring should be rotated to reveal one to two threads. Minimal resistance and drag will be present, though its minimal amount will keep the thread gage sturdy. The ring should then be rotated, further, into the truncated section. The produced drag will remain the same, though increased flank contact may render it slightly larger when fully engaged. This may be repeated for other thread gage sides, matching drag unilaterally and effectively calibrating each area.