The slim keg adapter (SKA) is a disk which slip fits into the hole of 50L keg stacker or spacer allowing either a 1/6 barrel or 1/4 quarter barrel keg to safely set on top of a half barrel keg. You just have to flip over the disk and place the keg size you want facing up.  It is designed to fit universally into our new half barrel keg spacers and stackers as well as retrofit perfectly into those already on the market.