[LargeFormat] How to measure thread sizes?

[Marco Milazzo]

Ye gurus,

I've acquired a few lenses and lens boards, and now I'm trying to join them.
Seems like I never have the right flange or the right retaining ring, or the
hole in the board to too big or small.  So. . .

How do you measure these things? What tools are needed?   Using a ruler
doesn't seem that accurate, and I'd like to be able to say, "I need a 409mm
flange," not "It's about 4.5 inches." (Not saying those are equivalent -- I
just invented them).

How to measure the diameter of rings, flanges and other holes?   Same
issue -- I want an exact measurement, not "About 3 7/8."

How about threads per inch -- is that an issue?

By the way, if anyone has extra flanges or retaining rings they want to get
rid of (i.e. sell), email me.  I'm looking for a bunch.

Thanks in advance,

Marco
El Paso, Texas (104 degrees last Thursday)