In international watchmaking jargon, strap refers to any non-metal bracelet: leather, rubber, nylon, fabric, composite materials. The distinction from bracelet — which is always metal — is operational, not stylistic, and has direct consequences for how you mount, replace, and maintain the piece.
The history of the term leads straight to 1973, when the British Ministry of Defence codified the single-pass nylon strap with the designation MIL-S-46383, STRAP, WRIST: INSTRUMENT. The NATO name doesn't come from an Atlantic agreement: it comes from the NATO Stock Number, the alphanumeric code by which British defence catalogued standardized supply materials. It's a detail I hear repeated incorrectly almost every day.
On the construction side, the most important variable today is the attachment system. Quick-release systems with spring bayonets — found on Seiko Astron, IWC EasX-CHANGE, Hublot One Click, Vacheron Overseas, Audemars Piguet Royal Oak Offshore Diver and many others — allow tool-free changes in seconds. Pay attention though: not all systems are equally accessible. On the Tissot PRX the bayonets are recessed between caseback and strap so tightly that the operation becomes frustrating. Drilled lugs — attachment points with through-holes rather than simple grooves — solve the problem at its root and simplify changing even without proprietary mechanisms.
Among strap types with their own history, the Bund deserves a note. It's a leather strap with a backing that covers the rear of the case: born in military contexts to isolate the watch from skin and reduce damage from heat or corrosion. It works best on cases with contained diameter, where the mass of the backing doesn't break the wrist proportions.
The rally strap has its origins in Sixties motorsport: perforated leather with multiple perforations along its entire length, designed to lighten and allow the strap to breathe during races. The Tropic-style is instead in rubber, with characteristic grooved profile, born for vintage diving and returned to fashion with the rediscovery of Sixties-Seventies instruments.
The term strap monster circulates among collectors to indicate a watch that looks particularly good on different straps, often because of clean lugs and neutral proportions. It's not a flaw: it's almost a compliment.