This is the large volume reducer for Fox Float shocks with the same dimensions. It reduces the the volume inside the air canister, which ramps up the spring rate.
It typically retails for $25, which I think is excessive. I would have set an even lower price, but the material cost that Shapeways charges isn't negligible.
When installing the spacer over the piston, the part will most likely crack since it does not have the same flexibility as nylon. This does not impair the functionality as you can see in my picture. For ease of installation press the spacer into the lower portion of the air sleeve until the surface is flush, and then close the shock.