What is for?T-Slot Aluminum Extrusion for 3D Framing.*price per meter* Specs:Material = AluminumHigh strength aluminum extrusion.A = 40 mmB = 15.7C = 8.6 mmD = 8.5 mmE = 6.5 mmF = 3 mmAluminum Guide Rail of Conveyor (40mm x 40mm)