The word CAP stands for protection. Sonia Center Pinch Caps are made of unbreakable plastic and are used to cover the front of camera lens, thus protecting it from dirt, dust, fingerprints & scratches. The advantage of this cap is that it can be fitted on to the camera lens without the removal of bayonet mount lens hood. It is always a good idea to have a spare lens cap in case you lose one while in the field or on vacation. Sonia makes quality lens caps at great prices.