This 1515 Corner is a type of connector for 1515 Aluminum Extrusion. It could help you fast-prototype a 1515 frame. The package comes with 90-degree corner connectors and screws, you can connect up to 3 Aluminum Extrusions on 3 dimensions and fixed them up with the screws.
exactly as described , so far so good. Its just a pity that 1515 extrusion has a 5 mm hole, so the screws are useless. Had to use M5 Helicoil to get its fixed .