I'm using rigid steel conduit with steel boxes where I have elected to
use the conduit as the grounding conductor. I have a 1/2" conduit
going into a masonry box with concentric 1/2 & 3/4 knockouts. I'm not
crazy about concentric KO's so I thought I'd knock out to 3/4 and use
a 3/4 to 1/2 reducing bushing where the conduit enters the box. (In
this case it would actually be an "expanding" bushing.) ... and a
locking nut on both sides of the
connection.

Isn't what I propose better than using the 1/2 knockout then praying
that the 3/4 knockout doesn't come loose? -- better for insuring a
good ground? The code does not say much about reducing bushings. I
really rather not run a separate grounding conductor.

--zeb