Swarovski Crystal Encrusted Magnetic Necklace with Crossed Racquets Ball Marker inset in the piece. This designer style necklace is so gorgeous that nobody would ever know you're wearing a ball marker! Any of your Navika 25 mm magnetic ball markers will pop in and out of this functional and fashionable necklace. Chain is adjustable between 18-20 inches and is stainless steel so it will not rust or tarnish.