This is a keg stand for stacking cornelius kegs on top of one another -- while leaving ball lock disconnects attached.

I use 2.5 gallon kegs in brewing, and with my 7" Keezer collar realized I had plenty of vertical space to theoretically fit two kegs on top of one another. When I attempted it in practice, however, the bottom keg had to be disconnected or the ball lock headers would prevent the top keg from stacking comfortably. This spacer adds the additional necessary height to allow sufficient clearance for the ball lock disconnects & beer/gas lines.