When drawing an assembly drawing, items such as screws, nuts, bolts, shafts need to be drawn. However, these items do not offer any new information but cutting them. Therefore, these parts are non sectioned parts. Even though a cutting plane may pass though them, there are left "in the round" or un-sectioned.

In 3DEXPERIENCE CATIA, you can specify whether a product should or should not be sectioned when generated into section views or breakout views using a drafting extension. Please watch the video to understand the way of doing it.