I was reading OceanicTime: ORIS ProDiver GMT and the last image reminded me:
That’s a nice clasp. If you look close, it has two side buttons, and when pressed you can lengthen or shorten the strap by about 1cm.
This is a brilliant feature and every strap and bracelet should have it.
Here are the ones I’ve seen, reviewed or coveted:
That’s the Girard-Perregaux Sea Hawk II, from my review on ABlogToWatch.com. That was the first time I had ever seen one, as as noted in the review, they’re a damned fine idea.
Rolex introduced their Glidelock (details here) and it’s on several of their models now:
I owned a Tudor Pelagos for a while; it has a superb clasp and adds a spring-tensioned mode; probably the best of any design I’ve used:
That’s not a great picture, here’s a better one found via Pinterest:
It’s more complicated but works better.
The Seiko Marinemaster SBDX001 I owned had one but I disliked it: too thick, sharp bits that poke the wrist and awkward to use.
Omega makes one too, part number 117stz001154, has quite a few fans:
IWC Mark XVIII (18) looks elegant:
Now, with all of those (and others that I’ve missed), you’d think that buying one would be easy.
Or at least possible. Nope. This is one of the very few that I’ve found:
Formex sells clasps designed to work with normal 2-piece watch straps. They’re pricy at $65 to $120. I’ve not seen one in person.
Hey watch companies: Please add these to every bracelet you sell! And the dive straps too.
Update: There’s now an entire site devoted to this, called https://tolmia.blogspot.com/ where ‘tolmia’ stands for ‘tool-less microadjust’.