A cylindrical piece to hold the PTFE tube of the E3D v6 (only this!!!) centered, when mounting the E3Dv6 hotend.Install the PTFE tube in the hotend and cut it so that it extends to the aluminum plate just right under the extruder gear. Clamp in place with supplied black mounting ring (without it, this piece is going to be too short).Form a funnel-like entrance on the PTFE tube with a sharp knife to allow for easy filament insertion. Now, push the adapter over the PTFE tube length protruding from the heatsink of the V6. Install everything in the extruder mount and push up until the adapter touches the aluminum plate mentioned already. Tighten the screw and you are done. M212 Z setting should be around -.6 to -1. Be careful setting this! You have to adjust this parameter or the Printrbot will destroy your new hotend / the bed.