Microdermals are also sometimes called "single point piercings" because they are piercings that only penetrate the skin once. The anchor, a flat piece of metal that sticks out sort of like a foot, is what holds the piercing in place. Sometimes the anchors have small holes in them, which allows the tissue to encompass the anchor as it heals, giving it a firmer hold.
There are two basic ways that dermal anchors can be inserted - with a regular piercing needle or with a dermal punch. The dermal punch seems to be the best and least traumatic way to create the hole for the anchor, but some states don't allow the use of dermal punches. They can still be done safely and effectively with the needle as long as it's done by a careful and experienced piercer.
Dermal anchor jewelry can be made with either stainless steel or titanium. Because titanium is often preferred for surgical implants due to its low rejection rate, it's also the optimum choice for your anchor jewelry. There's usually just one standard size with a variety of jewels to choose from. The jewel that is visible on the skin is threaded and just screws into place, so they are easily interchangeable once the anchor is healed. The twisting action involved in removing or replacing the jewel can damage the tissue if the anchor isn't healed, so that's why you need to wait.
Healing of this piercing usually takes 8 - 12 weeks.