What are lugs?

The lugs of a watch are part of the case, where the leather strap of bracelet is onto attached. The “lug-width” is the size measured in millimeters between two lugs, this information is useful when buying a new strap or bracelet. 

Common used  lug widths are: 

16mm, 18mm, 20mm and 22mm 

the Lugs of a watch by Benjamin Marcello