These can be used to stack Ikea Lack tables a bit more safe.

1 side has a hole in it that fits around the screw of the table, to make sure it can't move.

On the top, the leg fits quite snuggly into it. some small movement/pushing might be needed.

A small margin is used on the sides as not all Ikea tables have their holes in the exact same spot.

In case you want a remix where the top side is bigger or anything, post it in the comments and I will try to create a remix for you.