For circuits over 250 volts-to-ground, electrical continuity can
be maintained between a box or enclosure where no oversized,
concentric or eccentric knockouts are encountered, and a metal
conduit by
(a) threadless fittings for cables with metal sheaths
(b) double locknuts on threaded conduit (one inside and one
outside the box or enclosure)
(c) fittings that have shoulders that seat firmly against the box
with a locknut on the inside or listed fittings
(d) all of these