This is a replacement foot for the IKEA Lack table legs that have been cut down and shortened.  It is intended to be printed in a soft/flexible material like TPU and is made slightly undersized to ensure a tight fit to the hollow cardboard leg.  No glue is necessary to keep it attached to the leg, but you might have to bend/flex the corners and outer edge down slightly when attaching it to the leg to allow it to seat fully.

I have not tried it, but if you want to print it in a rigid filament like PLA, you might try scaling it up in the XY direction very slightly (~1%) to allow it to fit.