Lug spacing

Lug spacing is the internal distance, measured in millimetres, between the two pins on which the watch strap or bracelet is fixed to the case. It should not be confused with the external width of the lugs themselves: that is an aesthetic measurement, this is a functional one.

At the bench, I measure it with a sliding calliper placed inside the lugs, flush with the lower edge of the case, where the strap makes contact with the metal. A half-millimetre error here creates play, lateral tension on the links, or worse, a strap that won't fit at all. I've seen customers ruin new straps by taking the external measurement instead of the internal one.

The most common sizes today are 18, 19, 20, 22 and 24 mm. 20 mm covers most sports watches and medium-sized tool watches. 22 mm is frequent on more robust divers. 24 mm is historically linked to certain Swiss manufacturers producing large-diameter cases. Odd sizes like 19, 21 or 21.5 mm exist and complicate matters: the aftermarket for these widths is narrower, prices rise and choice shrinks.

A detail that technical specifications often ignore: lug spacing can vary slightly between the upper and lower lugs if the case is asymmetrical or if the manufacturer has designed a shaped strap. In that case, the relevant measurement is at the narrowest point, because that is where the strap must pass without forcing.

The English term lug spacing is the most used in forums and international catalogues. Lug width circulates as a synonym but technically describes the width of the lug itself, not the space between the two: the distinction is subtle but real. In Italian, passo delle anse and misura anse are also found—less precise but understandable.