Step 3: Completed Slitter
You can see the silver metal nut stuck in the glob of black epoxy.
The two tips just stick into the back of the camera when you press it in place.
The plastic key is a piece from a garden sign. It has a X cross section and works great for winding the film.
You can also use a car key.
If the blades ever wear out, or become dull, or out of alignment, you can usually pry the entire lump of epoxy out of the camera and start over.