These bicycle chainring bolt spacers are made of aluminum alloy, wear-resistance, strong tensile strength, rust resistance, high strength and sturdy. It is used for mounting single chain wheels as the double chain wheel bolts are too long to lock with a wrench. Fit for bicycle headset, stem and chain wheel change. Fine tune the chainring to get the perfect chain alignment. The internal diameter is 10mm/ 0.39inch, external diameter is 12mm/ 0.47inch, thickness is 1mm/ 0.04inch or 2mm/ 0.08inch. Package includes 10 pieces of bike chain wheel washers. Colour Silver Material Aluminum alloy Inner diameter 10mm/ 0.39inch Outer diameter 12mm/ 0.47inch Thickness 1mm/ 0.04inch / 2mm/ 0.08inch Part Type Washers Type Washer Brand Unbranded/Gener.