Which screw thread gage to get?

[Tin Falcon]

Part of the problem is there has been three metric standards, Indusry is attempting to consolidate to one ISO.

This quoted from a fastenal flyer.

The Metric System
One problem with standardizing the metric system is the initiative to fully convert metric specifications to
an ISO standard. Although the process has begun, most industries are unenthusiastic about converting
from DIN or metric ANSI.

It is things like this that lead to misunderstandings. and arguments.
Tin