thread pitch coincentricity

[RJT]

We are quoting some gage pins that have threads that will be ground between centers (from an outside vendor) and diameters that will be ground between the same centers, so I'm confident they will be concentric. However, what would be a method of checking this for an inspection report? The print tolerence is tight (.0003) as this is used to check positions of tapped holes to other features in our customers parts.
The only thing I can find are off lead thread arbors from Southern Gage. Any experience with them?