This may be a detachable part to support the micro motherboard and does not necessarily have its own DP/N.  In 5060M Dell calls it hdd caddy support. the best pic I find has the letter CAV1 on it.  you could try approach some of the eBay seller selling the micro motherboard and ask if they can sell you just the bracket for a reasonable price.  most micro motherboard buyer may not need that part, so maybe some seller is willing to part with that piece for you.  Or at least ask the seller if there is a Dell P/N sticker for the bracket.  I doubt it has one though. [IMAGE]   I am thinking in the old Optiplex 700 series there is a black plastic bracket for BTX heatsink shroud.  I have a few of those and I have not noticed any Dell DP/N sticker on those either.  
[IMAGE]Hello, I'm looking for information on the black plastic tab or bracket for the blue drive bay used in the MFF Optiplex. I checked and so far I haven't been able to get the part number. The manual identifies it as "black plastic tab" and no part number. I have a couple 7050M that it is missing.  Thank you, Chris
Optiplex micro (MFF) 3020M, 9020M, 7050M black plastic HDD tray clip