This takes the place of the uppermost 5mm spacer on a threadless 1 1/8" headset (i.e. just below the stem cap) to give a space for a bike computer to be mounted (using the normal handlebar mount). I've printed it on a Formlabs Form2 SLA printer, and it fits exactly as intended.
The STL file and the parent CAD file (Autodesk Inventor IPT format) can be downloaded freely from Thingiverse at
http://www.thingiverse.com/thing:2036128.