Cardboard Peak Flow Mouthpieces (disposable), Adult, 100/cs. Dynarex Cardboard Peak Flow Mouthpieces are disposable, single-use accessories designed for adult patients undergoing peak expiratory flow (PEF) testing. These mouthpieces are compatible with the Dynarex Resp-O2 Peak Flow Meter and are ideal for use in clinical settings, respiratory therapy programs, and at-home monitoring