This is a filament oiler and dust filter made for the Robo3D. Part of it extends through the slot in the plastic shell to avoid the problem of the filament abrading a groove into the shell as it feeds (see picture). Add a piece of sponge and some oil and it's ready to go.I probably don't need to go into much detail here. I like to fold a small piece of sponge in half around a piece of filament, then push the sponge in through the top of the filter. After removing the filament piece, there will be a cavity in the sponge to feed spooled filament through. I usually add 0.15 ml of Canola oil to the sponge with a syringe, but I'm sure a few drops is just as good. It doesn't hurt to put a little oil or grease on the wear surfaces of the oiler and the printer case.