<p>Front lens cap. Made of high quality aluminium alloy.</p> <p>Main advantages are:</p> <ul> <li>more strong than plastic</li> <li>can not fall off the lens accidentally</li> <li>protects a lens filter thread from damage if lens is dropped</li> </ul> <p>Drawbacks:</p> <ul> <li>takes bit longer to put it on/off than plastic snap-on caps</li> </ul> <p>So, this king of caps is the best for long storage or moving inventory, not for everyday work.</p>