I think the measurements on the websites are correct and should be a good guide. I don't have a 16 inch collar handy, but I just took a BBESF 16.5 inch collar out of the cupboard and measured it. The waist is 45, just as the BB website says. I also just measured a CT ESF 16.5 collar. It's 42 on the waist, just as the website says.
4/10/14 at 4:05am