Magnetic Fill Nipple Cover protects your HPA tank's fill nipple from dirt and debris and prevents that dreaded "hiss" that sometimes knocks your tank out of the game. Clips allow you to adjust the positioning of your HPA tank on your gun. If the gauge or nipple align in just the wrong spot, the clips act as spacers and will allow you to thread your bottle in securely while altering the position of the gauge and nipple.