BritKali is an exclusive jewelry collection to be used in collaboration with the Fitbit Flex device. The Fitbit Flex fits into the ID bracelet and all of the bracelets are interchangeable. Thus, you can build your own bracelet with nylon cording, leather or metal chain in different finishes and colors. The id bracelets are unisex and both men and women can pick and choose any options that strike their fancy. The Fitbit Flex device is sold separately, but fits into any of the BritKali items. For best results, please use the original Fitbit Flex band for working out and monitoring sleep.