This is an infill and support cube / cylinder for Cura. You can use this cube or cylinder to target SPECIFIC AREAS OR SPECIFIC PARTS for HIGHER INFILL. Here are the instructions:

1. Import your model. If you're gonna resize your model, do it now BEFORE continuing.
2. Unselect "Ensure models are kept apart" and "Automatically drop models to the build plate" in Cura preferences.
3. Import this cube or cylinder and resize as you go along if you want.
4. Select the cube or cylinder, and use the button "per object settings" on the left side.
   Select "Modify settings for infill of other models" and enable that setting.
   The cube or cylinder now turns transparent gray. Select "Per Model Settings" and change the infill that you wish to have targeted.
5. Place the cube or cylinder where you want it to go on the model to have a specific area or whole model changed.
6. Slice and print.

NOTES: check the images for easier how-to. In this example, I'm strengthening the keychain loop on this to 100% infill to make it stronger. The rest of the model stays at 20%. Of course, you can use ANY .stl you like to import as a "cube" or "cylinder." This just makes it easier for you.

This cube or cylinder can also be used for supports - a how-to manual coming soon. If you ask me technical questions such as the physics behind Newton's 3rd law in a vacuum with complex mathematics / electronic schematics - I cannot help you. Just follow these instructions.

CAUTION: do not try to multiply the cubes or cylinders after it's been changed with a different infill. This will crash Cura.