This is a quick feeder and vent setup I made for lost PLA casting.  For me, I print these, attach them to a 3d printed model I want to print.  Then coat it with joint compound, let that dry.  Encase it in sand with sodium silicate.  Let that harden.  Then pour in molten aluminum.  The aluminum melts/burns out the PLA, leaving a cast object.  I thought others might be able to use these.  You can print multiple of the vent and attach them to make longer feeders/vents.

For an example of this casting process watch this video put together by someone much better than I at it. ;)
 

Enjoy!