250mL Gas Sampling Tube, 4mm Stpk. Tube is designed for the collection and storage of gas samples. The 250ml tubes have a sidearm O.D. of 13mm, but with the addition of a syringe sampling port for use with a CG-3022-05 or CG-3022-22 septa. Supplied complete with one CG-3022-05 red rubber septa.