Electure,thanks for the pics! I was thinking "chase nipple,' but the OP dod say 'close nipple.'
A few other details need to be addressed.
First of all, many folks make their own short nipplez by cutting off a length of 'running thread.' While the NEC is silent as to using running thread into conduit bodies, it prohibits using running thread with threaded couplings.
"Chase nipples" come in different lengths, and the threads are straight (not tapered). This brings up two issues.
The nipples cannot be so long that they 'bottom out' before everything is tight.
Plus .... while the 'cheap' conduit bodies have straight threads, iron ones have tapered threads. Thus, it is possible that you will not be able to properly thread some fittings into some conduit bodies.
A chase nipple provides a nice, tapered throat for the wires to enter the pipe. A close nipple, by way of contrast, requires multiple lock nuts and a plastic bushing. I typically use them in combination with a threaded coupling, as when I have to attach a stem-mounted light to a box; I am not always able to rotate the fixture, and the coupling makes a much more secure mounting than attaching the stem to the box directly.