Enjary joint
From Brickwiki
The Enjary joint is a SNOT technique that joins two plates bottom to bottom. The Enjary joint was found and publicized by Didier Enjary, though he is not the creator of the joint.
The joint consists two plates and as many levers as possible. The flat ends of the levers are wedged between the tubes on the underside of one plate, and another plate is placed on top.