Two flanges engage the grooves in each end of the adjoining sections holding them securely together. Must be used on all sections of chimney that make up an offset. This includes two locking bands per elbow plus one locking band for every chimney length between the elbows. Must also be used on tees to attach chimney lengths. While locking bands are not required on other chimney lengths, their use is recommended to provide a more attractive finished appearance.