Glass is the expensive part of any optic, and these are the inexpensive parts that keep it clean and usable. Sunshades thread onto the objective to cut glare and keep rain off the lens; flip caps and slip-on covers protect both ends between shots; anti-reflection devices break up the glint an objective throws back in bright sun.
Athlon supplies the riflescope sunshades, sized for its Cronus, Ares, Midas, Helos, Argos, and Talos scopes, with Trijicon covering flip caps, slip-on covers, and the ACOG and MRO anti-reflection devices. More small parts in optics accessories, or shop rifle scopes.