Before we go, let's pull out the hard drive tray and take a look at the platter drive our mini came loaded with.

Tucked under the tray: a 500 GB, 5400 RPM HGST hard drive, coming in at 2.5" wide and 7 mm thin.

And on the top of the tray, a promising mounting point for a blade-style PCIe SSD, presumably what we'll find in a Mac mini equipped with Fusion Drive.

To test just how promising, we dropped in the SSD from our recently torn down 27" Retina 5K iMac (and used its mounting screw). Looks like a nice fit!