This Super Engineer II watch band is designing for 2009 onward Seiko Tuna models such as SBBN013 or other 21.5mm lug Seiko diver or sport watch case with straight lug. Super Engineer II watch band is composed by 5 chamfer edge well-made solid 316L stainless steel units. Screw-in adjustable details instead of pressure pins. Length adjustment is simple & easy via flexible screw details. This item includes one pair of FAT spring bar (Generic Seiko Dia. 2.5mm spring bar) to ensure a more secure connection. Accompany with V-Clasp double lock buttoned diver's clasp. V-Clasp was made from solid 316L stainless steel with extra 6 micro holes for flexible fine tune length adjustment. Featured in V shape safety lock, streamlined form & chamfer edged design to giving a more massive look. Chamfer double locks diver's buckle is ideal for watch band with thickness approximate 4.0 - 5.0mm thickness. Today replaces your Seiko Tuna into this unique aftermarket watch band.