seiko unisex's 18 mm wide black nylon band for seiko snk809, snk805, snk807, and snk813 seiko this 16 mm wide seiko unisex's watch strap is made of black nylon. the band thickness is 2.5 mm. this strap is compatible with seiko snk809, snk805, snk807, and snk813. length dimensions below do not include the buckle. add the length of your watch to ensure that this strap would fit your wrist. image for illustration purposes.