The Apple Watch Band V2 comes in 40mm or 44mm watch band sizes. Apple Watch faces come in many versions and sizes, but the band sizes that fit them split into two options. Here is the breakdown of what size band will fit which Apple Watch Face size.
The 40 mm band will fit 38 mm, 40 mm, and 41 mm Apple watch faces.
The 44 mm band will fit 42 mm, 44 mm, 45 mm, 47 mm, and 49 mm(Ultra) Apple watch faces.
Please note that each Linq Band V2 includes coordinating straps that can be configured for either S/M or M/L length.