We started using this when our dog choked herself on her collar during walks and it worked well but it is slightly too big for her so we have now got a smaller size.  Handbook says refer to website for measuring, and that medium is Neck 16-22 inches, Chest 15-28 inches.  Our dog is about 8Kgs so I think would best fit a dog several Kg's more.

It wasn't that clean so have put it through the washing machine on a cool wash and the orange has come up well, I can only see one dark spot.  Please note that the metal clip has lost a bit of paint, otherwise it seems in good condition.