A VERY LITTLE application of grease is useful for viton O rings. For non-crucial applications (joints on dirty vacuum lines processing large samples) finger grease works well. Otherwise, and for sliding rings on valves etc., we would recommend a single drop of TorrLube (Sputtered Films Inc., Santa Barbara). Its very expensive! Tim Heaton NERC Isotope Geosciences Lab Keyworth Nottingham NG12 5GG, UK E-mail [log in to unmask]