Unisex Chrome-plated Steel M Hollow-out Collar Restraint with Magnet Locking Pins.
The collar has one O-rings for attachment to chains, ties or other bondage gear. Means you can securely lock your sub to the toys of your choice. You can even attach a leash to the collar and lead your sub around and make them follow all of your commands.
The inside diameter is 12.0 cm, the width is 2.0 cm, the thickness is 0.5 cm