Summary

The Supermicro 825 2U chassis small riser card stabilizer (e.g. RSC-R1UW-2E16) as seen on https://www.wanhunglo.com/2020/supermicro-x9srw-f-small-riser-mounting-adapter-p24

If you can, please use the RSDOC (RS DesignSpark) file as that's my original source file. The STL is just an export that might not have had the perfect settings for your printer and/or application ticked or might even be incomplete.