Blender extrusion, normal direction, and the order of vertices

I wrote an article about Blender extrusion about a year ago. I now understand the logic behind extrusion, verticies, and direction of normals:

Order the vertices counter-clockwise and pull them up. The normals will be directed outward.

It appears like this is a common practice for usual CAD programs. Related articles:

Autodesk

The order of vertices around the face determine the direction of the face (whether a side of the polygon is the front or the back). For example, if you place vertices in a clockwise direction, the face normal points downward. If you place vertices in a counter-clockwise direction, the face normal points upward. See Create a polygon mesh.

FreeCAD Forum

  Vertices go clockwise around the normal direction.

No, they're counter-clockwise normally.

Stack Overflow

The vertices should be in counter-clockwise order when the vertices are viewed from outside of the object. (Obviously, viewing from inside the object they are then in clockwise order).

The normal should point outward.

File Format

This is a description about STL file.

• The direction of the normal is outward
• The vertices are listed in counter-clock-wise order from outside, obeying the right-hand rule.