These are amazing and I'm glad I took the risk on them. For the price they're at, they are wonderfully well made and will fit a variety of nipples. Although you cannot adjust the pressure, you can add weights to the string or simply tug on them for more delicious torture.
The most helpful critical review
Clover Clamps with a Bite
These nipple clamps are phenomenal. I love them so much and will be using them daily. I am into pain/pleasure and it's always nice to experiment. I definitely recommend these nipple clamps to moderate/advanced users. Beginners can have fun with these if they start slowly. This item, for the price, is definitely worth it. I couldn't be happier unless they were heavier, but you can always tie things to them. They do not come off if tugged and it does leave you sore the next day; it's a good thing.