Blender 2.8 Modeling a technical piece

My complete training: https://www.udemy.com/blender-279-complete-training-from-beginner-to-pro/?couponCode=BLENDERMASTER9 3d printing with Blender training: https://www.udemy.com/blender-279-discover-3d-printing/?couponCode=PRINT10 Reference Image: https://www.dropbox.com/s/5uf9jxxlmj7y2mb/piece%203d.zip?dl=0