The 1954 Chevrolet distributor does not have a nut inside the distributor (I do not know about earlier or later distributors). In fact, the bolt and nut that hold the two bakelite-plastic insulators together (on either side of the distributor body) are a special bolt with no head on the inside of the distributor and the "nut" on the outside of the distributor that tightens the two pieces of plastic together has a round head. The round-headed nut has grooves for a special distributor "nut driver". This head of this round nut barely protrudes beyound the plastic. A normal hex/ignition nut is used to tighten the ignition wire againts the round "nut".
This is probably clear as mud - I will see if I can find the parts in an old distributor and take a photo or two.
I doubt if the bolt, plastic pieces, and/or round nut can be obtained from a parts store (or even a dealer). A used parts dealer is the most likely source.
The special nut-driver for the round nut used to be available from NAPA. Some people cut a slot in a flat scredriver blade to have a tightening tool (described by someone in an old posting on this website). (This is most likely what stevesr is referring-to above)
Tim
