Custom cassette spacers for Shimano and SRAM compatible systems. 6061 t6 aluminum, I stock .5mm, 1mm, 2mm, 2.5mm, 3mm, and 3.5mm spacers. The inside diameter is 34.7mm. I can make any other thickness you may need within reason with a typical tolerance of +/- .05mm, for the same price. Please specify what thickness you need when ordering.