So I was at one of the sites that has the 5250 AIO today, so I opened it up, and no, it does not have the SSD screw. I'm shocked! Not. The standoff for 2230 is also missing, you'd have to move the 2280 to the 2230 position. That's OK, I plan on adding a 512GB which is usually 2280.
So you're saying the correct screw that goes inside the standoff screw to hold down the SSD is M2 x 3 mm?