I don't doubt that some fittings, especially those for products other than rigid conduit, have straight male threads. But tapered threads are specified for the ends of conduit.
From Wheatland?s website:
Wheatland?s Galvanized steel Rigid Metal Conduit (RMC) is manufactured in accordance with the latest specifications and standards of ANSI ® C80.1, UL-6, and federal specification WW-C-581. The pitch of RMC threads conforms to the American National Standard for Pipe Threads, General Purpose (Inch), ANSI/ASME B1.20.1. The taper of threads is 3/4 inch per foot (1 in 16).
And the NEC specifies tapered threads for field threading:
344.28 Reaming and Threading. All cut ends shall be reamed or otherwise finished to remove rough edges. Where conduit is threaded in the field, a standard cutting die with a 1 in16 taper (3/4-in. taper per foot) shall be used. FPN: See ANSI/ASME B.1.20.1-1983, Standard for Pipe Threads, General Purpose (Inch).