This is an insert for the Lee case collator that separates the 9mm cases from the larger ones. It's just to do a final check so that a .40 doesn't get stuck and you have to remove the whole thingamajig to get it out.
Since 3D printers can be a bit finicky I've added a "SAMPLE" module (https://www.thingiverse.com/thing:3380383) so that you can check the width of the sieve holes to ensure the correct function of the insert.
The object uses the following parameters:
RES = Resolution. This is just the polygon count, set it higher to get nicer curves. I wouldn't go over 100.
CDA = Case Diameter Adjustement. The most important variable, it sets the width of the sieve holes. I've found that with my printer setup a 0.5mm CDA is just enough to let the 9mm cases go through and keep the .40 out. Adjust this according to your setup, you might need to insert a negative value.
STN = Sieve ThickNess. This is to set how thick you want the object to be. I'm fine with 2mm, but you might want a sturdier or lighter sieve.
Since this is a large area print I'd recommend using a raft to ensure that the model is easily removed after the print.