Stainless Steel Clamp On Chimney Rain Caps do it all; while they are an attractive way to cap off your metal or clay liner, they are also very effective. Protect chimneys from rain, snow, and animal intrusion. These caps clamp on to the outside of the opening of the chimney with a secure one screw fastener. Measure the outside diameter of the metal or clay liner and select which size range your measurement is in using the drop box below.