This pen has the two line imprint and paddle overfeed. Yet it appears to have a normal slip on friction fit cap.
If you look more closely, it is a large straight cap. But instead of seating on the section, it seats past the section onto a straight portion of barrel. The stop serves as a stop for the cap. The posting end is straight, not tapered and the step also serves as a stop on that end. I believe that this represents a hybrid cap style from the small straight cap to the traditional cone cap. The imprint date and feed seem to justify this assumption that it might have been a style in transition from straight caps to friction fit “cone caps”, as the pen predates the traditional friction fit cap with conical shape inside.
