I'm a props artisan and make a ton of molds for a lot of different materials.  Quickly built mold boxes are usually not very material efficient, and material efficient boxes take more time to make.  This set allows me to slam together a custom mold box in seconds that conforms closely to the shape of the object I'm casting, saving time and expensive casting materials.  All you need to do is use binder clips to hold the pieces together, and then I usually hot glue the bottom to a piece of hard board.  I can usually just pull the binder clips and break away the wall after the pour is cured (always use the correct release agents for your casting materials!) If I break a wall piece, it takes 15 minutes and a few pennies to print a new one.  

I attempted to add as many unusual pieces that I've needed for some of the most challenging situations I've encountered.  Be careful with the interior corners, you may have to get creative with how you apply your binder clips.  

I use PLA+ to print these, if you use a resin make sure there is no chemicals in the resin that will inhibit curing of your casting material (the way sulphur reacts with many silicones). Resin will probably make your de-molding process easier without all the layer lines grabbing at the casting material. 

I included 50mm and 100mm tall sets.  You can always scale up, just make sure you use the same scale for every piece to get a good fit.  

When I need to cast taller pieces, I usually build my box perimeter upside down, then a second box right side up and use the flat base of each to glue them together with hot glue to get a second story on the box. 

Over the years this has saved me hundreds of hours of set up.  I hope others find it useful and lend their creativity with new pieces and remixes.  I have thoughts on how to make them properly stackable but that will have to wait for a version 2 I think. 

(Don't forget you can build your box in your slicer to get a count of how many of each piece you need before you arrange the pieces efficiently.)