... looking for a source for thread centers. This device threads into an internal thread and give you a surface to measure from with a height gage or a CMM probe. ... my search on the internet has turned up a big fat ZERO.
Hi CarolX;
As is frequently the case, I come late to the Cove

, but I hope I will provide valuable information.

For full disclosure, let me begin by stating that my company sells what you have called Thread Centers.
This item is known in the thread gage industry as Threaded Hole Location Gage or Threaded Hole Centerline Gage. An internet search on either term will yield better results.
There are five types of this tool, each has its problems and all should be used with caution, regardless of the manufacturer’s claims. None of these tools are defined in any ANSI specification so design, dimensions, tolerances and effectiveness will vary from manufacturer to manufacturer.
The five types are:
1.
Flexable
2.
Solid, Trade Names: Tru-Pos and JoPlug
3.
Tapered
4.
Lead Lock
5.
Variable, Trade Name: Multi-Ball
I did not know if I should post the data about each style. The data gets a little wordy, so I have imbedded a web link into each name above. The link will that give you more detailed information and photos of the
Threaded Hole Location Gages.
I do not think that I have identified all the existing trade names. If someone wants to add more trade names, please do so.