PrintABlok is a system designed by 3D Printing Professor. It consists of stackable, buildable blocks in a variety of shapes; all of standardised sizes, and is very (and I do mean very) open to extension. The so called BaseBlok is 16x16x16mm, and that's the default unit; 16mm.
For more information, see https://www.printables.com/model/47788-printablok-base-bloks
I was building happily and found that I wanted wider, longer, and stronger. I also opted to go for very sleek finishing panels.
You are gonna need the connector of the original, see its files section: https://www.printables.com/model/47788-printablok-base-bloks/files
The author remixed this model.