The wonderful world of watch straps — leather, rubber, NATO or otherwise — is endlessly varied. Though many types defy classification, it's helpful to know some common terms and varieties related to that essential part of any band, bracelet or strap: its buckle or clasp — in other words, the hardware that helps you actually affix a watch to your wrist.
Most fastening methods can broadly be broken into two varieties: the buckle and the clasp. There's more or less one kind of buckle, but there are several kinds of clasps each of which can also have variations associated with it. Though often overlooked, the features, comfort and quality of this hardware can factor into the value of a watch. Here are the important terms and types you need to know:
Pin / Ardillon / Tang Buckle
You can probably just call this style a "buckle" without any confusion, but you'll see it referred to as "pin buckle" (relatively intuitive) as well as "ardillon" and "tang." What you need to know is that all these names are referring to the same simple system which essentially functions like most belts that hold up your pants. They can come in all kinds of shapes, finishes, materials and sizes, but they generally feature a bar, a frame and a pin which goes in the holes on the strap's other end. The remaining length is tucked into the keepers.
Keeper: The loops, usually of fabric, leather or metal, which keep the long end of the strap from flapping around. Most straps have two, but some feature only one keeper.
The most common type of fastening method used on metal bracelets is the folding clasp. In its most basic form, it features two hinges and three sections which fold over each other and snap shut — some varieties can simply be pried open, but this is less common in modern watches. There are multiple variations and solutions regarding ways to prevent the clasp from accidentally opening, several of which are discussed below.
Watch enthusiasts have been known to brawl over whether the correct term for this type of clasp is "deployant" or "deployment." We'll let the forums hash that out. What's important is to know that it's similar to many folding varieties found on metal bracelets — but used on straps. The benefit is said to be less wear on the strap material than is caused by bending between a buckle's pin and frame over time. Depending on the example, drawbacks can include a bulkier wearing experience and the minor inconvenience of needing to slide it over your hand since the two strap ends remain connected.
A butterfly-style clasp can be found on metal bracelets or deployants. Rather than three pieces of similar length which fold over each other and close at one end, a butterfly has a longer piece and two shorter pieces that close in the middle. This is usually considered an elegant look and is often found on formal and high-end watches.
This type of clasp is rare and might not even really have a name, but it'll be clear why we're calling it a seatbelt style. A tab in one end inserts into the other with a click, but this can be tricky to do with one hand.
Hidden clasps keep the mechanism on the inner part of the bracelet or strap and out of sight, often resulting in the appearance of an unbroken band. Ideally they're thin and unobtrusive.
Clasps with push-button releases will typically feature one or two spring-loaded buttons on the side(s) of the clasp that need to be pinched together. Requiring more deliberate action from the wearer, this is a generally safer method than one that simply pries open.
Commonly found on folding clasps, a tab that folds over the main clasp locks into place to offer additional security. It must first be opened in one direction before the clasp itself is opened in the other — and it can be combined with, say, a push button system for added safety.
This is an additional feature found on some dive watch bands. A small tab on the underside of the clasp can be unfolded to offer additional length, its original purpose being to fit over a wetsuit. A similar but superior type of extension is a ratcheting version that can be operated with buttons while the watch is being worn. It's a handy feature even in day-to-day situations when you find that your wrists have expanded due to climatic changes.