joints
thingiverse
Look closely at the design scaling feature - it's initially locked but can be unlocked using Cura. Note that I don't have copyright privileges, which is why I'm recommending Tinkercad instead.
Download Model from thingiverse
With this file you will be able to print joints with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on joints.