Cosmo Darts White Case-X Holder. This holder is designed to fit onto all Case-X Dart Cases. Made from a high quality plastic in a White colourway with Case X branding on the front. Easy to use just slide onto your Case X and keep your darts with you on the go.Cosmo Darts Black Case-X Holder. This holder is designed to fit onto all Case-X Dart Cases. Made from a high quality plastic in a Black colourway with Case X branding on the front. Easy to use just slide onto your Case X and keep your darts with you on the go.