Precious Plastic is an awesome open source effort to make small plastic-recycling machines readily available to folks around the world. If you don't know about it, check out PreciousPlastic.com for more info.
This extrusion screw is a special type of screw designed specifically for extruding plastic, the expanding inner thread puts pressure on the plastic as it melts, providing pressure for higher detail.
Normally extrusions screws are strictly industrial- extremely large, hard to source, and extremely expensive. PP designed this version designed specifically for home-scale extrusion, but they only shared the file as an STP and IGS file, not an STL. So I just converted it to STL, and posted it here. Use at your own risk.
In order to work, this part needs to be metal, not plastic. I'm sharing it here because I suspect that this part could be printed in PLA and then lost-PLA cast in Aluminum. If so, this will make a very difficult to source part much more accessible.
It could also be CNC milled on a lathe. Go nuts! If you learn something, be sure to share!