Nipples are strange critters. Some men hate to have them messed with, others (like me) crave it and others are, meh. I've always loved playing with my nipples and having them played with. It's very much an individual thing, no one-size-fits-all. I use clamps some but to be honest the best tools I've found for really intense half-hour sessions are wooden clothespins. It takes a while and experimentation to find ones that are just right as they can be waaaaay too strong. My routine with the clothespins is about half an hour. I lay back and put the pins on and just let them warm up for about 10 minutes. After 10 minutes I begin twisting in different directions and pulling different directions. After they've heated up the sensation is intense right on the edge of pleasure and pain. Maybe too intense for some. At the 20 minute mark I release the pins quickly which causes a rush of pleasure pain. I immediately apply some hand cream on each one and let them cool off. After a short cool-down time I give them a good finger massage first lightly and then deep. I most always finish off with masturbation and a good solid orgasm. The nips stay tender and tingly for a couple of days after a session. Intense nipple work isn't for everybody but I love it.