This NBR rubber watch band with a curved end lug perfectly fit Seiko MM300 Prospex Marinemaster SBDX001, SBDX003, SBDX005, SBDX017 models, etc. The lug of this watch band was tapered into 18mm buckle size, added value on flexibility of using your original 18mm Seiko MM300 buckle. NBR rubber has superior strength and more resistant than natural rubber to oils and acids. Material has met the RoHS requirements and rarely causes severe allergic reaction. Cut to size to fit most wrists. Accompany with ratchet buckle clasp which is an ideal wetsuit watch band buckle. The ratchet theory extension mechanism is of great importance both for convenience and for safety. This item also includes one pair of FAT spring bars (eg. generic Seiko Dia. 2.5mm spring bar) to ensure a more secure connection. NBR rubber watch band is a good choice of Seiko replacement watch band for your MM300 Prospex Marinemaster SBDX001, SBDX003, SBDX005, SBDX017 models.