These are replacement o-rings for the Blichmann Boil Coil but can also be used on the RIMS Rocket. Over time, these can wear, and excessively rough cleaning techniques can cause them to break or more commonly get lost. Never put off brewing due to a lost or broken o-ring again! This kit comes with two replacement o-rings for a Boil Coil. Very handy to have on hand in case of a brew day emergency!