This adapter enables mounting of monitor with [HP QuickRelease Bracket 2] with 40x40mm holes to [VESA 75mm x 75mm] stand.
Info about HP QuickRelease Bracket: https://www8.hp.com/h20195/v2/GetPDF.aspx/c06264645.pdf
PS. picture shows 5mm too long plate, little mistake - I didn't reprint it because it didn't matter but the model is fixed.
The author hasn't provided the model origin yet.