Indiana Standards Laboratory has the best standards for calibrating your Thread Micrometers and Thread Micrometer Setting Standard.
Calibration range of (1 to 6)in or (25 to 150)mm for your Thread Micrometer Setting Standards. Our best measurement uncertainty is 42 µin or 1.1 µm.

These micrometers have a pointed spindle and a double V-anvil, both shaped to
contact the screw thread. The micrometer reading therefore gives the pitch diameter.

Starrett Screw Thread Micrometers, Model 575, 585, 575M, 585M.
Starrett Screw Thread Micrometer Standards 
Mitutoyo Screw Thread Micrometers, 326-351-30
Mitutoyo Screw Thread Micrometer Standards, 167-261

For measuring external threads.