Thread Plug and Ring Gages, Hardness Testing, Calibration and Special Taps and Dies at WESTport

WESTport provides Precision Measuring Tools at discounted pricing. We hope you will find
this added value service saves you time and money as your one stop shop for Quality Assurance Products and Services.

Precision Tool Specials

Gage Tip of the Month - Calibrating Thread Plug Gages

For our purposes here we are going to examine the measurements of Outside Diameter (OD), often referred to as the Major
Diameter, and Pitch Diameter (PD). These are the two diameters most laboratories measure when calibrating your thread plug
gages.

The OD measurement is taken directly over the threads and is therefore not a great problem in calibration. Its function is to
check the cleared diameter in the thread to be checked.

The Pitch Diameter is most accurately measured using the three wire method. It should be noted that certain difficulties or
process procedures may result in higher uncertainties. Some examples of practices that may result in higher uncertainties or
even inaccurate readings are: Using elastic bands to hold the three wires, not using proper force on the wires, or using the
wrong size wires.

PROCESS:

1. Thoroughly clean the thread plug gage. If possible use an ultrasonic cleaner to remove the tough dirt that hides in the
threads.

2. Exam the threads for nicks or material stuck in the threads. This is especially a problem if gaging aluminum or cast iron
parts.

3. Allow the gages to "soak" or acclimate to a temperature of 68°F to 72°F. This soaking process takes about 24 hours.
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