Watch straps come in endless variations, but a few styles have gone down in history as classics. For sporty and rugged watches, there are NATOs and rubber dive straps, as well as various kinds of bracelets, of course — whereas leather in its myriad forms is inevitably the choice for a formal look. But leather straps don't have to entail dressing up — these three styles, for example, have unique history and are meant to be paired with hard-wearing tool watches.
A significant proportion of pilot's watches today are based on those used by the German air force during WWII called, collectively referred to as B-Uhren. They're incredibly popular and can be worn on all kinds of straps, but you'll sometimes find them on leather with rivets, just as they would've been worn in the cockpit all those decades ago. Often made with rather thick leather and contrast stitching, these straps feel genuinely rugged. The studs fasten a folded section of the strap, though some versions simply use stitching — in either case, both look distinctly aviation-themed and perfect for pairing with pilot's watches and leather bomber jackets (scarf, goggles and a leather helmet are optional).
The origins of the racing or rally strap are unclear, but the benefit of breathability provided by perforation is evident — especially in the summer. In motorsports, certain automotive parts such as steering wheels and brake pads would historically have holes punched in them in order to reduce weight. "Rally" straps — as well as driving gloves and certain other accessories — have co-opted this aesthetic, and the resultant look is killer. The most distinctive rally straps have several large holes, whereas others have multiple smaller ones. All work great with sporty vintage watches, and chronographs in particular.
The bund strap has a funky style that could only be born of a practical application. It consists of a patch of leather, either in roughly the shape of a watch case or as a wrist-wrapping cuff, through which another strip of leather is threaded. Since it's so bulky, the bund is a great way to help a small watch wear more prominently.
Like the aviator strap above, the bund is associated with WWII pilots, and it gets its name from the German Bundesrepublik, or Federal Republic (though there's evidence of its use even earlier). The extra layer of leather was useful for keeping a watch's metal off the skin in the extreme temperatures of early cockpits. In the 1970s, bund straps were sported by various style icons and enjoyed some popularity — it's how Paul Newman wore his famous Daytona, after all. The bund hasn't made as strong a comeback as other '70s watch styles yet, but maybe it's time to give it a try.