The illustration below is from a 1905 Gillette advertisement.
The threaded stem on the cap engaged the inner handle.
In the 1964 movie Goldfinger, we get a close look at Bond's shaving gear.
He uses a Gillette slim handle adjustable razor when he is shaving in Goldfinger's plane on the way to America.
A slight twist of the handle could expose more or less of the blade edge as the cap sqeezed the flexible blade against the guard.I have shaved with a Super Speed from 1954 and another from 1960 and I could detect a definite difference, with the ’54 being noticably smoother. You can see a list of codes, along with some other notes and information, HERE.Schick Krona Though Schick was mainly known for their Injector razor, they also produced a DE razor from 1959 through 1965, the Krona.However it is generally (though definitely not universally!) agreed that it’s engineering probably peaked around 1955 (some extend that to about 1960).After that I think engineers began to “over tweak” the design and the accountants began to get more involved in the production process.