When ordering gas cylinders on our website, we recommend the correct cylinder threads for that specific size cylinder at the bottom of the page. If your meter has a pump attached for active sampling, a demand flow regulator (DFR) will be the correct option. If you have a personal meter, one that uses diffusion (no pump), a fixed flow regulator will be the correct option. Typically 0.5 Liters per minute (LPM) is the correct flow rate, but if needed, flow rates from 0.1 LPM to 6LPM can be ordered. If you currently have a bottle and need to know the correct model regulator, just click on the “ASK US!” button and send us a picture and we will quickly let you know the correct model needed for your specific cylinder.