How to Find the Depth of a UNC 2.5'' Threaded Bar

Web search and you will find this, although it says that the UNC is 4 TPI for that size.

For sharp 60° threads, √3/[2(tpi)]. However, normal thread forms have flattened/rounded crests and bottoms so that it is much easier to look up in a table rather than apply a formula.

It's depth, with one e.

I suppose measuring it is out of the question?

Machinery's Handbook, any edition.

Thread Types - James Glen

Thread Types, Forms and Pitch | Anzor Stainless Steel Fasteners ...

There are three constant pitch Un series: UN8, UN12 and UN16. In this series, the pitch remains constant regardless of the diameter.

For a 2.5 inch fastner, UN8 has a major diameter (predictably) of 2.5 inches. The minor diameter is 2.3512

look up UN8 thread.