This is a Wall Control centerpiece compatible with the DDD system for socket extensions. 

• 5x: 1/2" (16.2mm diameter holes)
• 12x: 3/8" (12.3mm diameter holes)
• 5x: 1/4" (9.0mm diameter holes)

Used with a left/right 2x3 angle bracket.

Printing suggestions:

• 1.2mm of wall
• 15% infill
• PETG if you live somewhere hot/humid

See the lovely DDD system here: 

aderusha/DDD-Printable-Wall-Control-System: DDD Printable Wall Control System, 3d printable organization solutions for Wall Control pegboards