The lug on a watch is a part that attaches the case to the strap. It allows the strap to be changed more easily than if the case/strap were fixed together.
A watch that has lugs would have two at the top of the case and two at the bottom. They're commonly used and there are a number of different types with varying designs and widths between them. We go into more detail on what they are and the different types below.
How watch lugs work
The lugs are typically fixed to the case at the top and bottom, above the 12th hour and below the 6th hour, and have a mechanism to attach the lugs to the watch strap.
Lugs can work in several different ways. Often another part called a spring bar is used. This is a metal rod that has extendable thinner parts at both ends slightly thinner than the middle part attached to springs. The spring bar attaches a watch strap to the case, where the middle part goes in-between the two lugs on each side of the case and through a loop in the strap.
The strap can be removed/attached by pushing the ends of the spring bar in, allowing the middle bit to be removed or positioned in-between the lugs. Once attached, the spring bar can often be retracted using a tool from just beside the band on the inside of the case, so watches using these tend to only have holes on the inside of the case. They may also have quick release mechanisms on the strap with a button/slider allowing it to be removed more easily without a tool. For these types of mechanisms the strap/spring bar tend to be fixed together.
A solid metal bar may also be used, without extendable parts at the ends, where the lugs may have holes on both sides allowing it to be fed through. Lugs with holes on the outside might have caps that can be added/screwed into the case at both ends of the lug to hold the bar in place. For spring bar configurations, the middle section tends to be wider than the ends and so this is less prone to falling out (but the ends are slightly thinner and extendable, so not as durable as a solid metal rod, so there are pros and cons to both).
You might also get lugs that have a bar fixed rather than be removable. This type of lug might be used alongside a NATO strap for example, where the strap goes through the rectangular gap rather than attaching using a spring bar. See our article on types of watch straps to learn more about them.
If your watch has lugs with a spring bar and you're considering changing the band, be very careful. When adding/removing the lugs, the watch case is prone to getting scratched. You might also scratch/bend the lug itself. In either case it risks the band not being securely/properly attached to the case and potentially falling off and also causing visible damage/ruining the aesthetic. You can get specialist tools to help minimise scratching/denting.
What is lug width on a watch
The lug width is the space between the two lugs on each end where the strap would go, so this width determines what types of straps you can use for a particular watch.
You can measure the width of a strap yourself, or it might have markings on it to indicate the size. The lug width is typically measured in millimetres. The part of the watch strap you'd need to measure is the width at the end where it attaches to the lugs. When measuring the width of the strap, make sure you measure the strap width rather than the bar.
Watch lug types
Lugs work in several different ways, where they might be used alongside a spring bar or solid bar, or the lug/bar might just be fixed together. The aesthetic of lugs can also vary, where there are a number of common types used. An example type might be a straight lug, where each lug is a straight rectangular shape when looking at the watch face.