RE: Where to install SSD in Optiplex 9020 SFF
The ssd caddy sits inside the 3.5 inch caddy and holds 2 drives like a matruska doll. One on top and one underneath.
The Optiplex 3020 7020 9020 R494D 2.5 inch caddy fits inside the DN8MY 3.5 inch blue caddy.
The Silverstone adapter has all the mount points of a standard 3.5" hard drive, and it's only $8 with free shipping. It holds two 2.5" devices stacked.
So the SSD Adapter caddy is 0R494D