Ciao, these are engine mounts that I made for use with RtA70kit design. You can find it among my drawings ( https://www.cgtrader.com/3d-print-models/hobby-diy/mechanical-parts/high-pressure-fan-rta70kit-rc-models-and-other )
They are for the version of the 75mm cover.
Size details in the pictures, if you want use for other things. There are two versions for motors with 24 and 25 mm diameter. Have fun.
In the video explain and test.