A design inspired by @KupgughIronTusk 's https://www.printables.com/model/396942-ipad-pro-129-under-desk-slide-mount for what hardware I had

Dimensions

• Overall dimensions: 143 mm wide, 207 mm long, and 21 mm high. 
• The area where the iPad sits is 123 mm wide, 187 mm long, and 5 mm high, leaving a 16 mm height clearance for your device.

Note

• Three holes on each side.
• Each hole is designed with a 10 mm diameter for the screw head and a 5 mm diameter for the screw shaft.