The cut is explained at point 3 in the mounting instructions:
side guides (when the insect screen rolls up vertically);
superior and inerior guides (when the insect screen rolls up horizontally with high bottom truck);
superior guide (when the insect screen rolls up horizontally with low bottom truck).
After cutting the aluminium profiles, it is required to "staple/crush" the brushes.
It is an important and necessary point for the proper functioning of the insect screen. In fact, by stapling/crushing brushes and aluminium, brushes immediately get locked and don’t interfere with the locking mechanisms of the insect screen, which suffers the effect of vibrations over time.