These light plastic nipple clamps can be very securely attached to the nipples. They can be adjusted very precisely and weigh very little, so the amount of pressure they exert can be very precisely tuned. However the stationary bar has spikes which will insure a tight hold and some piercing sensations. They come with a ring attached by a metal chains. Specifications: Fully extend the two bars are spread .75 inches apart. The clamp measures 1.5 inches in width.