In the 1968 NEC, Article 346 there's a note at the top of the page:

Quote
Where conduit is threaded in the field, it is assumed that a standard conduit cutting die providing 3/4" taper per foot will be employed.


I don't have any copies of the NEC 1957-1965, but it didn't appear in the 1953 NEC.


From Allied Tube & Conduit's website:

Quote
....The 3/4" taper NPT threads (ANSI B1.20.1)
are full cut and hot galvanized after cutting....



The SCE Overhead Service Requirements state that GRC or IMC conduit be used for a mast, so there's no water pipe allowed, at least down here in So Ca. (Sierra Pacific's Requirements say that "Periscope service entrance per NEC, Article #230 and must be approved by SPPC prior to installation") I don't imagine that it would be the same anywhere else.