These high quality stainless steel beautiful collar which built-in a padlock with two keys.The collar finished in nature brushed surface handmade.we guarantee the material we used entirely stainless steel (other than the brass padlock) Please be extremely careful when closing the collar. The hinge has the potential to pinch as you are closing the collar. Internal diameter CHANGE to circumference are:10cm(circumference 31.4cm,12.36'' inches),11.7cm(circumference 36.5cm,14.5'' inches),12cm(circumference 37.6cm,14.8'' inches),13cm(circumference 40.8cm,16'' inches),14cm(circumference 43.9cm,17.3'' inches),15cm(circumference 47cm,18.5'' inches).