These are Wheels Manufacturing Headtube Spacers. They are for properly spacing the stem and top cap on the headtube of any 1-1/8" standard threadless steerer tube bicycle. Each spacer can be stacked in combination with the same or other thickness spacers to acquire proper spacing and stem cap compression. 2.5 and 5mm spacers are in packs of 5; larger sizes are sold individually. Specifications: Color: Carbon Material: Carbon S.H.I.S. Stem Clamp Diameter: 28.6