Check the listing for details. 4.5mm TINY Sterling Silver MAGNETIC CLASP 1/2" Chain Extender 5mm Spring Ring US. Color: Silver, Condition: New with tags. Listed at 9.75 USD. THESE ARE VERY SMALL!!! Please be sure you have an understanding of just how small they are.Stronger and larger are https://www.ebay.com/itm/155111030150 This clasp is: 4.5mm diameter X 15.5mm overall including 5mm Spring Ring clasp 3/16" X 19/32" it will extend chain 1/2" a dime coin is 17.5mm Open ring will fit Spring Rings & up to 10mm Lobsters In our opinion, suitable for chains up to 25grams. You be the judge for yourself. No hassle returns. It is strong enough to hold one side & slide all around the Nickel without it even starting to come apart. Spring ring WILL be slightly attracted to magnet, as will other clasps. Their internal springs are steel. Rest assured these are solid Sterling Silver NOT responsible for any damage or losses due to clasp failure. USE AT YOUR OWN RISK if you use a PACEMAKER, INSULIN PUMP, OR DEFIBRILLATOR etc...Thanks Weight: 0.65grams DO NOT clean Magnetic Claps in ULTRASONIC cleaners as it will reduce the strength of the magnets.