The STACK-A-LACK is an adapter to stack IKEA LACK tables on top of each other. No screwing, no glueing, just stacking. It wasn't designed to be very sturdy, but it should keep the top table from sliding off.

There is also the DOUBLESTACK-A-LACK connector that can be used to combine two LACK stacks.

If you want to stack two LACKs, print the STACK-A-LACK plate. If you want to rack two stacks (four LACKs), print the RACK-A-STACK-A-LACK plate if your bed is large enough, or both the STACK-A-LACK and the DOUBLESTACK-A-LACK plates.

The RACK-A-STACK-A-LACK plate contains the adapters for all four corner and the two middle connectors.