This bracket is used to connect 3 extrusion pieces into a 3d corner such as the vertex of a cube. You are required to use an M12 tap to bore out the end of the extrusions into which you insert the included bore reducer. Then just bolt the bracket on with an M6x20 bolt. Ideally you want to use a bolt with the DIN 7991 head style but it doesn't actually matter too much.