This is a genuine Casio metal core band MK2. It was removed when I customized a new GW-B5600BC. Please rest assured that this is not an imported product claiming to be genuine. The metal core band is made of resin with metal inside to create a high-quality feel. It is lightweight and has a buckle, making it easy to put on and take off. The design is different from the GW-M5610UBC, with a flat surface without protrusions. The material is resin, but Casio calls it Fine Resin. Casio doesn't specifically name the bands, but to avoid confusion, I'll call it MK2. Here's the manufacturer's description: -- "The outer links of the band have metal parts embedded in Fine Resin, and Fine Resin is also used for the center links. The design has been finished to pursue a glossy texture." -- The length can be adjusted easily by yourself, as each link is connected with spring bars instead of split pins. Included accessories: Genuine dedicated spring bars, 1.8mm diameter pin, 0.8mm diameter (difficult to obtain) Spring bar removal tool and link adjustment tool Compatible models: GW-M5610 (Module number 3159) GW-M5610U (3495) G-5600E (3160) DW-5600E (3229, 1545) DW-5600UE (3525) The original spring bars are 2.0mm in diameter and cannot be used. Conditional compatibility: GA-2100 (5611) The quick-release spring bar pin diameter is 1.2mm. The included spring bars will be loose. Please prepare separate spring bars. I believe this is the best price, so I will not offer a discount. If you want to buy it cheaper, please consider the GW-M5610UBC compatible version made entirely of plastic (market price is around 2,000 yen).