The "D" design on the cap is the same as one of the 28/29 styles. However, it is the external threads that are a conundrum. They would have to turn into a wheel opening, and there is no flange to tighten up against. Lance did a few modifications on caps on some of his cars. Maybe someone else did also. Hope we get to the bottom of this.
Pile of car manufacturers made under letter D in the complete encyclopedia of motorcars 1885 - 1968,
Could they be Desoto caps ? Detriot Electric as the pic I have shows small caps on wires as does Dixie ?