These are used to support and lock-in ¾" (19mm) thick shelves. The round peg on its rear face fits pre-drilled holes in the cabinet. Four of these support a shelf which is lowered from the top of the supports. This pushes in the tab, which snaps back to lock the shelf in place.

I originally needed these to replace ones that came with the cabinet but got broken when I tried to rearrange the shelves. These are born from a need to learn Fusion. I originally created a similar object in FreeCAD and can make that design available if anyone wants that. The FreeCAD version is smaller, but supports the same size shelf.

You may need to used the cad file to change some dimensions, such as the peg diameter or the height (thickness) of the shelf you want to support.

I have printed this both on an A1 and an A1-mini. 

Edit: I was notified that the .3mf file was removed because there was no printed image. However, the second image in the profile was a photo of two of the shelf supports. I can't promise they won't take it down again. Sorry for anyone who tried to download the file only to find the .3mf file was missing.  I have appealed (and uploaded the .3mf again).