Toggle clasps are two-piece clasps that are attached to opposite ends of a piece of jewelry. One section of the clasp is formed into a circle or other shape with an open center. The other half is a thick bar that attaches to the components at the other end. When you insert the "T" into the circle extends past the circle's edges to hold the jewelry in place.
Toggle clasps are widely used to secure bracelets and anklets, but jewelry artisans also incorporate them into their necklace designs. They are available in numerous sizes and designs. Toggle clasps are not as secure as clasps that have a lock-type closure.