It is E-Series Micro Mounting Assembly which uses standard VESA  mounting hole bracket for Dell optiplex Micro

bracket is compatible with the following systems:

• OptiPlex 3050 Micro Form Factor
• OptiPlex 3060 Micro Form Factor
• OptiPlex 3070 Micro Form Factor
• OptiPlex 3080 Micro Form Factor
• OptiPlex 3090 Micro Form Factor
• OptiPlex 5050 Micro Form Factor
• OptiPlex 5060 Micro Form Factor
• OptiPlex 5070 Micro Form Factor
• OptiPlex 5080 Micro Form Factor
• OptiPlex 5090 Micro Form Factor
• OptiPlex 7050 Micro Form Factor
• OptiPlex 7060 Micro Form Factor
• OptiPlex 7070 Micro Form Factor
• OptiPlex 7080 Micro Form Factor
• OptiPlex 7080 XE Micro Form Factor
• OptiPlex 7090 Micro Form Factor

https://www.dell.com/support/manuals/en-us/optiplex-3000-desktop/optiplex_7000_mff_accesseries_guide/optiplex-micro-pro-2-e-series-monitor-mount?guid=guid-6eaec021-4f12-453c-862e-7b4c4e740e88&lang=en-us

Ok everyone on Ebay has it listed for the 3020m 9020m series? Do you know if it will work for the 20 series?

This part N4XY2 works for 3020M 9020M

https://www.sears.com/dell-gyrt153186729-n4xy2-genuine-oem-dell-optiplex-3020m/p-A107014168