Muskrats or other vermin do not belong in your boat’s wet exhaust. They chew on hoses and at worse can cause your boat to sink. These muskrat guards install in the exhaust tube without drilling. To measure for the correct size, determine the inner circumference of your exhaust and divide that number by 3.14. Or if your exhaust is perfectly round, simply measure the inside diameter. Aluminum and stainless-steel construction. For exhausts 3 ½” up to 8”. Priced and sold by the pair.