Clasps, the part of your organiser that acts as the closure to keeps the organiser closed and your pages in their protective cocoon. The design has changed quite a bit over the years, they have become part of the style of the organiser.
Four Filofax organisers from different eras. Top left a Filofax York. It has a thin clasp with plastic popper cover. Moving across a Cavendish from a few years later, similar width but slightly thinner leather with a leather covering of the popper button.
In the lower row we move in to the recent era with a Holborn, the clasp has a slight taper to it and a full leather outer. Then finally the Malden I know not everyone likes the clasps on these mainly because they use the same dimensions from Mini to A5. Yes they do look a bit big on the Mini! This time we are back to a shiny metal engraved popper.
OK another four, from three different manufacturers... so who copied who I really don't know, all very similar in design although the execution is slightly different in each case.
Starting again in the top left we have a Van der Spek they have used this design as far as I know for quite a few years. Then a Launer from the 1980's this was made in England again similar design but being quite old it is quite supple now.
Then in the bottom row we have two Gillio's the Mia Cara on the left and an Amica on the right. The Mia Cara attaches the clasp to the outer 'jacket', so the organiser part doesn't have it's own clasp so the clasp is quite chunky. The Amica is a little more conventional and similar to the Van der Spek and Launer in the task it has to perform.
Personally I like the broader clasp as shown in the bottom four and of a generous length too so when you add in additional contents in addition to the pages on your rings the clasp closure doesn't feel strained like on the older thin Filofax ones seem to.
What is your favourite style and design?