This pair of nipple clamps is connected by 12" of chain. The 1" long thumbscrews are fine-threaded for precise adjustment of pressure, and will not fall out even when the clamps are fully loosened. The "grabbing" surface is approx. ¾" long by ¼" wide.
This is good-ol' kinky ingenuity in cold hard metal. The chain is easily removable with pliers if you so desire.