These powerful magnets are made especially for jewelry clasps. They have a large diameter counterbore that goes 0.125” deep into the magnet and then a smaller hole that goes the rest of the way through, this allows the user to thread a string then tie a knot on the end so the string won’t slip out. These durable nickle plated magnets are sold in pairs, a north and a south facing polarities, so they will attach to each other correctly. Please give us a call if you have any questions about your application (888-727-3327)