This is an eccentric nut (aka a decentration post) to adjust the pressure on your wheels for your 3D printer carriages or other moving parts.
Design is based on...Show more the item sold by robotdigg.
If you do not care to wait for the shipment to be delivered to your doorstep, just print it!
You will need 3 eccentric nuts like this to build the nice delta designed by Hadyn Huntley - Kumu-3D printer design: http://www.kumu-3d.com. In fact, 6 of those eccentric nuts, if you also use the back plate on the carriage for extra rigidity on the Kumu design.