What is the dog chain worn by the trendy girl around her neck?

Women's metal collar with the letter m.

Male metal collar without M-shape

Women's round neck+send storage bag+send chain traction

Men's metal collar

Stainless steel specifications are as follows:

Collar: wall thickness: about 6 mm.

Collar width: 2cm

Inner diameter: female 12cm, male 14cm.

M-neck without hollowing out: wall thickness: about 5 mm