Casio G-STEEL Carbon Core Guard Structures Mens Watch GSTB300-1AG STEEL models that feature Carbon Core Guard structures. These new models adopt tough G SHOCK styling with a disk indicator at 6 oclock that shows the current mode and charge level, and a front button that completes the overall rugged look. The disk, a round graphic digital display between 1 and 2 o'clock, and a digital display as 12 o'clock add to both functionality and looks. The GSTB300 model comes with a resin band. Shock Resistant Carbon Core