Human nipple tissue male and female are the same. The male tissue just does not get as big. One thing to remember is that nipples are tough and can take a lot of abuse. BUT they can be damaged quickly if used in the wrong manner.
Circulation. There needs to be SOME blood flow in and out of the nipples or the tissues will start to die in about 30 minutes. This means tight rubber bands need to be released after 30 minutes or the surface and underlying tissue will start to die. What develops is something called Deep Tissue Injury which is a term designed to convey the fact that underlying tissue has been deprived of oxygen long enough for the cells to have anorexia.
Clamps compress the tissue making it difficult for the circulation to be efficient. Again after 30 minutes anoxia starts to set in and cell death and break down occurs. This is not an opinion it is medical fact. The reason that many people do not have problems is going to be listed below. HOWEVER any time you deprive tissue of fluids that carry oxygen you are risking permanent cell death.
One way to avoid damage to the nipple over long term play is to toughen the area. The body can develop tissue that is harder when the same kind of stress is applied over and over and over to one area. In Martial Arts this is called body hardening and it is done to deliberately allow the participant to become somewhat less prone to tissue damage when heavy blows are given to the area. You can see this in movies where the "grasshopper" is beating his forearms and hands against a pole that is wrapped in rope. The area will bruise then heal and bruise and heal and eventually a type of scar tissue will result that makes that area of the body less vulnerable to tissue damage. Ask someone in the lifestyle who has been around in the 50's about the term leather butt. That is the same thing.
Back to how to avoid damage. Take your favorite nipple clamp and apply it for 15 minutes. Then remove it and leave it off for 5, then rotate the clamp and put it back on for 15 minutes. Rotate means turning the actual clamp so the main "clamping part" is putting the primary pressure on an area 90 degrees different from the original area. This has 2 results, Number one it hurts (not a bad thing) and number 2 it compresses a different area giving the original area a break and the opportunity to heal (also a good thing). You can do this over and over and over until the nipple is too tender to touch. Give the nipple 2 days to recover and do it again. Eventually you will have a nipple that is tougher and can support a clamp that holds much more weight and also can stay on for up to 30 minutes safely.
Now you might say "I put clamps on or wear them for hours and nothing ever happened." You are lucky. Tou can cross the Expressway blindfolded at rush hour and not get hit... again you are lucky. It only takes once to need surgery to fix something that could be avoided. Understand this body tissue NEEDS oxygen to survive. When it is cut off from the supply of oxygen the tissue WILL DIE. That is a medical rule that can not be avoided. For some the tissue is more resilient and can go longer. You do not know how long until it is too late.