I wanted to visualize how a typical hotend works, but it's very hard to see inside an actual one. Here's a complete model with threads, but it also includes cutaway versions so that you can see inside. Everything fits/screws together.
I've printed this at 300% so that I could use it in my video explaining how a hotend works and show the correct way to install/change a nozzle. You can watch it here:
I've used supports only for the nozzle and the heatblock.