.DRU File Extension
What is a DRU file?
A DRU file contains design rules created by CadSoft EAGLE, an application used for designing Printed Circuit Boards (PCB). It stores design rules for manufacturing a PCB and includes settings for layers, distances, size, shapes, masks, and clearance.
NOTE: Autodesk EAGLE was formerly known as CadSoft EAGLE. The software was acquired by Autodesk in 2016. EAGLE stands for "Easily Applicable Graphical Layout Editor."