To replace a screw-type clasp on a string of beads, work on one end at a time. Snip off the old clasp, leaving as much cord as possible. If there’s no knot next to the last bead, make one. Then thread the cord through the link in the new clasp and knot the link against the last knot in the string.
Trim the cord, leaving a length equal to the width of the last bead. Apply water soluble glue to the cord end and let it dry until it is stiff. Then use jeweler’s pliers to insert the cord end through the hole in the last bead. Leave only the knot showing. Dab epoxy cement on the knot and let it dry.
To replace a spring-ring clasp on a necklace or bracelet, simply open the end link of the chain or the jump ring that holds the clasp by grasping it with two pairs of flat-nose jeweler’s pliers and twisting it open at a slight angle. Remove the old clasp, put on the new, and close the link or ring by moving its ends together again.