I added codes that handle octagonal print bed. I haven't implement the angle and bolt hole calculation which determined by size of the equilateral triangle.
Aluminium extrusion: 20.00 x 20.00 (mm)
Size: 35.00 x 60.00 x 15.00
M5x15 Hexa cap screw x2
M5 nut x2
M4x10 Hexa cap screw x1 (Optional)