Early wrist-worn timepieces, from occasional eighteenth and nineteenth-century bracelet watches for women to the trench watches of the First World War, were generally converted or purpose-built pocket-watch-style cases fitted with wire lugs — simple soldered or brazed loops through which a leather strap or a fabric-and-leather 'shrapnel guard' style strap could be threaded, often with a hinged protective grille over the crystal.
Wire lugs are structurally minimal: two loops per side, sometimes formed from the winding pendant's wire stock, adequate for a light case and modest strap tension but limited in how securely they anchor a strap under repeated pulling. They are strongly associated with early conversions and early purpose-built wristwatches from roughly the 1900s–1910s.
Fixed solid lugs, cast or machined as part of the case rather than added as separate wire loops, became standard as wristwatches moved from a wartime expedient to an accepted everyday object through the 1920s. They allowed stronger spring bars, wider straps, and case designs where the lugs were an integral part of the case's aesthetic rather than an afterthought.
Lug width and spring-bar attachment (a spring-loaded bar between the lugs, compressible for fitting) became a de facto standardisation point industry-wide, since it determined which straps a given case could accept; this standardisation happened gradually through common practice rather than through a single published specification, and exact adoption dates vary by manufacturer.
Strap materials followed available industrial materials as much as fashion: leather and fabric dominated early production, expandable metal bracelets appeared between the wars and expanded after, and synthetic materials arrived from the mid-twentieth century onward; the strap or bracelet on an old watch today is very often a later replacement rather than original equipment, and should be assessed and described separately from the case and movement's own history.
Because lugs and strap-fitting hardware are functional and exposed, they are also frequently repaired, re-soldered, or replaced entirely on a working watch, so unlike a hallmark or a movement signature, lug form is useful for placing a case within a general period and style rather than for precise dating on its own.