We have noticed that the sensor part numbers can be a bit tricky to find on your MSA gas monitor. This is especially true of discontinued monitors. I wanted to share with you all a spreadsheet that I use every day when it comes time to order new sensors for the service department. Open up the Excel document attached to this post to get a breakdown of the various sensors used in common MSA gas monitors. I realize that this list will need to be added to and filled in a bit more completely, but this should cover the most commonly used sensors and detectors. I hope this helps you all out.