a taper pin is 2.900 inches long, the diameter of the large end is .375. what is the diameter of the small end

Answer 1

Standard taper pins have a standard taper, 1/4 " to a foot, so you can calculate the difference, or use the tables, giving you approx .315" for the small end. But, there are no standard taper pins with a large end of that size, so it may not be a standard pin, in which case the above may not apply.

Answer 2

Taper pin information sheet found at:

http://pages.cthome.net/errol.groff/Tapers.htm

Answer 3

I suppose it could be anything from almost zero to .374999r., You may be leaving out other data. Would you like to re-phrase the question?