Vitalograph Elliptical White Filter 33.5 mm OD for Sensor medics

Disposable Vitalograph Spirometry Fitter for Carefusion, PK Morgan, also fits over the QRS Orbit Pneumotachs, so you can eliminate cross-contamination. It has an elliptical mouthpiece and a 33.5mm OD. They come in a box of 50, and are indivdually-wrapped.

The filtration efficiency is 99.999%