Extension leg for barbeque grill

My barbeque has its legs from squaretube 20x20 mm, but are too short. So I designed this insert to accept a M6x100 screw and another piece to accept a M6x18 long nut.
This way I can raise the barbeque but also compensate for uneven terrain.

There is also a drill template to insert a screw in order to make sure the insert does not go deeper inside.