OK the Press Stud as they are also called, has been around a long time and in use on Filofax organisers since they were invented as far as I know? Some organisers haven't used a press stud on the closing strap, some use a fancy latch closure like the Deco.
They used to be marked with the makers name PRYM, but these days they appear to be marked with Filofax, so may be they buy them in enough numbers to get their own name on them.
So let's get up close....
So the press stud comes in two halves, the female bit in the picture above, and the male in the picture below. I will let you work out why I've called them that, without getting rude! But it follows the usual plug and socket rules... think about it.
So with me so far... in the picture is my Chameleon. Notice which part of the press stud is located on which part of the Filofax organiser. So now we switch to my Malden.
Now your turn to play 'spot the difference'.... apart from one is black and the other is red!
OK time is up... notice how the male and female bits of the press stud have swapped places... No I don't know why either...
A quick check of my mini collection and the Finchley is the same as the Chameleon. The three Maldens are all the same as in the picture above. Finsbury is the same as the Malden, likewise my old Winchester is the same as these two.
It of course doesn't matter, but I was just intrigued when I noticed the difference!!
Now before you go away... on the inside of the strap you might notice three letters embossed in to the leather very close to the main body of the organiser. For instance on my red Malden they are 'SIV' and VBV on the black Chameleon. These we believe are quality control letters to identify batches of organisers or similar. I won't claim to have discovered these.... that honour goes to someone on the Philofaxy Flickr Discussion Group back in 2008.
They aren't unique so you can't use them as a serial number, but it might be useful to make a note of the letters if you ever send a Filofax back for repair, you would know if you get the same one back again or not.