This is a kit consisting of a 2x20 stacking header and 2x 10mm nylon spacer. It allows you to mount an RPI2v2, RPI3v2 or RPI4 onto a Raspberry Pi fitted with one of the heatsink cases as seen in the photos.
Using the two supplied 10mm spacers together with the washers and nuts included with your original module you can support the bottom edge of the PCB against the heatsink. Optionally for the best possible support you can glue the spacer to the heatsink if you wish.
The photos here show an RPI2v2 fitted to a Raspbery Pi 3 and an RPI3v3 fitted to a Raspberry Pi 4.