On the requirements section of your response you write about 3-wire measurements on checking the pitch dia. at front middle and back with the pitch being the same size. Is this determined by the gage itself on what style it is? Say, a Hi/LO truncated thread set plug? Shouldn't all thread set plugs have a Low pitch dia. at the truncated major dia. end and at the Full form major dia. end be High pitch dia. not the same size pitch the complete length of the threads?
When purchasing Set Plug Gages there are three styles available:
Full Form Set Plug Gage
The Full Form Set Plug Gage is used for setting a Variable Thread Comparator (also known as a Tri-Roll Gage). It is also used for setting adjustable style thread ring gages when the thread form is truncated to a point that a Truncated Set Plug Gage is not desirable.
Truncated Set Plug Gage
The Truncated Set Plug Gage is the gage of choice for setting Adjustable Ring Gages.
HiLo Set Plug Gage
The HiLo Set Plug Gage can be used to set an Adjustable Ring Gage, but it is also excellent for checking Adjustable Ring Gages without the requirement of resetting them. The HiLo Set Plug Gage could also be used as a Check plug gage for a solid style ring gage.
When measuring the pitch diameter of a Full Form Set Plug Gage (or a Work Plug) the pitch diameter measurement should be taken at three points along the length of the gage. The resulting measurement will alert you to any taper in the gage, or any wear in the gage. The front end of the thread gage usually wears before the back of the gage as the front sees more work against its test piece.
When measuring the pitch diameter on a Truncated Set Plug Gage you may desire to check the pitch diameter at six points: Front/Middle/Back of full form portion and Front/Middle/Back of the truncated portion. Some will tell you that this is overkill, and they may be very right.
When measuring the pitch diameter on a HiLo Set Plug Gage the front half of the set plug gage has a different (smaller) pitch diameter than the back half of the gage. In this case you need to check Front/Middle/Back on both portions of the HiLo gage.
I am sorry that I did not fully understand your question, but I hope the data given is sufficient to answer your concerns.
