Maminbot 46 mm or 1.8 inch exactly. So you will need a slightly larger bore with some gap as leeway. However bear in mind that the barrel does not come with a tensioning mechanism so you may need to pack it with some foam, otherwise it may rattle about. The surface cap diameter overhang is 67.8 mm or 2.67 inch.

Maminbot The 3 USB sockets are directly attached to a circuit board with a switch mode power supply. It's all contained in the tube below the surface.

Maminbot I have plugged it in (220V) with an adapter (3-pin UK), device pumps out 5.10V, with no significant heat build-up. But that is without load. Customer service rep also seem to say it's a universal AC-DC transformer inside (see my review teardown pics). I'm still going to change out all the caps for better ones though, just to be safe. Or maybe someone would send this over to one of the electronics YouTubers for review and mod.