Has a 2mm opening in the Silicone grommet that securely holds the cording that you thread through it. The outside barrel is made of hypoallergenic brass, electroplated and nickel free. This clasp is popular when used to replace the macrame knot and when creating a simple adjustable necklace or bracelet.
Basically, a string-on clasp is a stopper bead and the soft silicone grommet won't damage any of your jewelry making materials.
We use this clasp with smaller chains, as well as our 1mm cotton cords.