Which small components are sewn inside a collar to ensure it remains flat against a man's collarbone?

Collar stays are small components typically made of plastic or metal that are inserted into the collar of a dress shirt. Their primary function is to maintain the structure and shape of the collar, ensuring it lays flat against the collarbone and does not curl up. By holding the collar in place, collar stays enhance the shirt’s overall appearance, contributing to a polished, well-groomed look.

Other options such as collar shields, studs, and clips serve different purposes. Collar shields are used to protect the collar from sweat and stains. Studs refer to decorative fasteners that can secure collar points or embellish a shirt, while clips might be used in other contexts but do not serve to stabilize a collar. Therefore, the correct answer is indeed collar stays, as they are specifically designed to support the collar's structure.