Those plastic Simplex outer wing nuts are from the 1960s. They had only brass hex nuts molded into the plastic and they too could easily unscrew. So, a small spring was placed between the two parts to function like a lock washer, holding the two pieces together with the plastic outer wing nut acting as a lock nut. Not entirely necessary once the skewer lever was engaged, but when a wheel was removed the single knurled metal end-nut could easily unscrew out of it's properly set position.
Because there was room allowed on the skewer length for the outer wing nut, the skewers will stick out considerably when the plastic part is missing. It does look ugly and unfinished (and always seems to find a exposed shin). The plastic itself became brittle over time and could easily crack or shatter completely sometimes leaving only the small brass hex nut from its core as evidence that it had once been in place.
Later one-piece end nuts with integrated plastic wing nuts - as on 1970s and later Maillard skewers - had plastic gripping the skewer threads (functioning rather like Nylock-type simple hex nuts) to help keep that single end nut from unscrewing. By the 1970s when Simplex had finally adopted Campy-style skewers, millions of the remaining older type skewers were down-graded and commonly found their way onto the cheaper model Peugeots. Now those skewers can be worth far more than the entire surviving bikes on which they may be found.
I always find it fascinating when I encounter an instance like this early type of French problem solving - which once again suggests that French designers and manufacturers acted as if they were coming up with isolated technical problems and solving them uniquely, as if they were totally cut off from the influences of all other foreign technologies.
The classic example of this would be the design of most any vintage Citroen automobiles. Someone had once written that French cars seem to have evolved as if they had developed in a parallel universe, one similar to ours in most every way, but untouched by any influences of the technologies of our own world.
