Casio Men's G-Shock Master of G Series Gravitymaster GR-B300-1AJFProduct Highlights The GR B300 is a GRAVITYMASTER timepiece that utilizes the characteristics of carbon material used in aircraft bodies, such as impact resistance, rigidity, and durability. It features a shock resistant structure called the "Carbon Core Guard Structure," incorporating carbon fiber reinforced resin in the case and a seamless bezel inspired by next generation aircraft, creating a powerful form befitting the GRAVITYMASTER series.