This is a device to protect the finish on the neckpipe of your trombone. From another viewpoint, this is a device to protect your neck and shirt collar from your neckpipe. An unlacquered neckpipe neckpipe sometimes leaves green marks on a player's neck, or on his wardrobe. This is made of a clear plastic tube with a slot along the long axis. It's designed to snap onto the neckpipe and is easily removable. Do note that the slot can have sharp edges, so be mindful of the potential of scratching during installation. You can wrap a piece of paper around the neckpipe, install the protective tube, then remove the paper.