Designed to protect barrel threads when not using a muzzle break, flash hider, or suppressor. Keeps you from loosing your crush washer. Also prevents debris from going down your barrel when not in use. Sold as a pair. These caps are designed for barrels that are 1/2" in diameter. The caps are made from vinyl so they are flexible, durable, and make a tight seal. All of my products are made and shipped from the USA. If this is not the right size you are looking for I have other sizes available. The color is black. I offer free shipping to the United States.