These long link chain collars are supplied in the UK by company who have been manufacturing chains since 1870.
Sizes available are as follows:
51cm/20", width 4mm
56cm/22", width 4mm
61cm/24", width 4mm
66cm/26", width 4mm
The collars are measured from the outside of one end ring to the outside of the other end ring.
To determine the correct size, measure your dog's neck and add 2" to 3". Double-check by measuring round the widest part of the dog's head to make sure the chosen length will fit over his head (allow about 2" for the end rings for a 3mm chain, a little more for a 4mm chain).