Often known as a “reed protector” but commonly called “chanter caps,” these simple plastic devices fit onto the end of your pipe chanter once it is removed from the bagpipe. The small, white screw is used to tighten it onto the hemp. You’ll often see these with a hole drilled into the top, but I think that defeats the purpose, which is primarily to preserve some of the moisture the reed has taken it. Most pipers remove their chanter from their pipes when they put them away. If you don’t, the reed will soak up any moisture that has accumulated inside the chanter stock. Also, if you have a moisture control system with a chanter tube, removing the chanter prevents your having to bend it into an angle that will damage the tube.