A gripper is what holds the skin onto the DTR bell or retainer.
They're made from silicone baby bottle nipples that are BPA free.
There are two versions of grippers, Solid or holes.
They can both be used by themselves or together when using different methods with the DTR.
The grip works by friction. Simply put when the skin is rolled onto the bell and the gripper rolled onto the skin. The skin becomes held by both the bell and the gripper, when force is used such as tugging or dual tension the skin gets pulled as if it is being pulled off the bell, When this happens the gripper gets tighter since it clings to the skins surface and tries to moves with the skin. Since the gripper is tapered like the bell the gripper can not slide off the bell with the skin. This action holds the skin tighter to the bell. The more tension the more grip.
Gripper removal is easy, first invert the gripper so that it's flipped inside out just as you would if you are about to attach the gripper to your skin.
Just pull on the gripper and work it over the collar portion of the DTR Bell.
Continue to work the gripper by stretching it over the collar
And finally work the gripper over the nylon screws ( if they are being used ) grippers will stretch quite a bit and it's pretty difficult to rip one.
To reinstall the gripper just reversed the process.
The Hole Gripper with holes I personally find to be more flexible.
The Solid gripper fits tighter.
The removal of the material to create the holes also makes the gripper more flexible.
The only drawback with using a gripper with holes is when you remove the gripper you'll see small little bumps on the skin as shown in this picture. These small bumps quickly disappear and I personally have never had any discomfort in using them although.
Some men prefer the solid gripper instead because it can be more comfortable because it does not have the small holes.
It really comes down to a personal preference on what someone prefers. Most men when purchasing a retainer will choose the solid gripper.