SMALL
Fits neck sizes 10.25" - 15"
Collar Width: 3/4"
Works with the SMALL DOG iD

MEDIUM/LARGE
Fits neck sizes 14.5" - 22.75"
Collar Width: 1"
Works with the MED/LARGE DOG iD

X-LARGE
Fits neck sizes 18" - 28.5"
Collar Width: 1.25"
Works with the XLARGE DOG iD