Bike Boost Hub Conversion Adapter Washer 5mm Black : Front Hub Adapter: 15mm Boost front hub adapter converts a 100mm x 15mm front hub to 110mm x 15mm Rear Hub Adapter: 12mm rear hub boost adapter converts a 142mm x 12mm front hub to 148mm x 12mm Material: Made of aluminum, which is sturdy, rust-proof, non-deformation durable Included: This kit includes 1 pc hub conversion, 2 pcs spacers and 6 pcs screws Easy to use: Comes with essentials, easy to install and convenient to use Specification: Item Type: Bicycle Hub Conversion Adapter Material: aluminum alloy sizes: Hub Conversion Size: 3mm: about 44x3mm/1.73x0.12inch 5mm: about 44x5mm/1.73x0.2inch Spacer size (Dia. outer x height ): 3mm: about 18.9x3mm/0.74x0.12inch 5mm: about 21x5mm/0.83x0.2inch Screw Size (Dia x H ): about 9.9x17.4mm/0.39x0.69inch contains: 1 bicycle hub conversion adapter 2 spacers 6pcs screws