What does “Lug Width” mean?

Lug width is the distance between the inside edges of a watch's lugs, measured in millimetres. It sets the width of strap or bracelet that will fit the case. Common sizes are even numbers such as 18, 20 and 22 mm, but some models use odd widths such as 19 or 21 mm.

Getting lug width right is essential when selling straps, bracelets or watches that will be fitted with a new strap. A strap that is too narrow leaves gaps and looks wrong, while one that is too wide will not fit at all. Lug width can also change between generations of the same model, so it is worth checking the exact reference rather than assuming. For example, a newer version of a familiar sports model may have moved from 20 mm to 21 mm. When measuring, use calipers between the lugs where the spring bar sits.

A buyer's message might read: “What's the lug width on your watch? I want to put it on a 20 mm leather strap.” Including the measurement in the listing saves that back and forth.