Some people love nipple clamps. Some people do not. If you want to try using them with your partner, you need to first establish if he has sensitive nipples. You can do this by playing with his nipples in a vanilla setting first. Try brushing them with your finger, nibbling on them, or sucking on them. Note your partner's reaction. Some people will love it, like X does. Some people, like me, will think you're wasting your time. But give it a shot and see what your partner thinks.
If your partner likes the brushing and the nibbling, you can then experiment with pressure - pinch a nipple and see what reaction you get. You should also try twisting. If your partner likes both of these things, you're probably ready to try nipple clamps.
Note: Start easy on the pressure! You don't want to shock your partner. Go gradually harder, noting reactions as you go. For some people, there is such a thing as "too much." For others, you can't go hard enough. Feel free to ask your partner if it's good.
If you're ready to try nipple clamps, but you don't know what to try, the best thing I can recommend is to pick up some clothes pins from the super market. You can get them pretty much anywhere. The only downside is they come in something like a 20 pack and you only need two. If you can figure out a use for those 18 extra clothes pins, let me know. According to X, the clothes pins are gentle. They also have a broad tip, which is useful for securing the nipple and for providing even pressure.
There is a technique to using nipple clamps. Here it is:
Pinch the nipple with one hand and pull it away from the body slightly. With your clamp, come from underneath the pinch and attach it to the nipple. You want to get as much of the nipple in the clamp as possible and this is the best way I've found to do it.
When releasing the nipple, pinch it from underneath the clamp and hold that pinch as you take off the clamp. Keep the pinch for a few seconds before gradually releasing it. This prevents the blood from rushing back too fast, which can be jarring and even a little painful.
That's it! Give it a shot!
I don't actually have any products to recommend, other than the clothes pins. While X technically has a set of "official" nipple clamps, he doesn't like them very much and I've never used them. But if you're going shopping, look for something with a strong spring and a wide tip.