The Airlock Dock & Stacker slide onto the lid of the PolyDryer™ Box and are held with a friction fit. The airlocks can be press fit into the dock and are also held in place with a friction fit. The Stacker version allows you to stack multiple PolyDryer™ Boxes on top of each other and the tabs on the 3D printed part make sure the boxes are aligned nicely.