10 Sets Silver - Fit Hole Diameter: 8mm / 0.31"; Under Head Size(Female): 8 x 18mm / 0.31" x 0.71"(D*L); Under Head Size(Male): M6 x 30mm / 0.24" x 1.18"(D*L); Hex Socket Width: 4mm / 0.16" 10 Sets Black - Fit Hole Diameter: 8mm / 0.31"; Under Head Size(Female): 8 x 15mm / 0.31" x 0.59"(D*L); Under Head Size(Male): M6 x 35mm / 0.24" x1.38"(D*L); Hex Socket Width: 4mm / 0.16" Application - Fit for all kinds of DIY, leather crafts, clothing making, or as a fastener to connect two objects. Such as thin photo albums, leather bags, wooden board connections, etc. Installation - Make a hole between 0.5-1mm larger than the diameter of the female rod, put the screw and nut on both sides of the locked object, and select the appropriate tool to lock it. Advantage - Precision mechanical thread, made of carbon steel material, high hardness.