The First Tactical Oxygen Kit connects an O2 cylinder to the First Tactical ALS/BLS bag/box. It also works great for snapping an O2 cylinder on to many other manufacture’s ALS/BLS bags. I am a volunteer paramedic in a rural area and use another manufacture’s somewhat compact EMS bag as my ALS jump bag and if I’m going to need O2, I can easily and quickly clip on the First Tactical Oxygen Kit to my ALS jump bag and carry it into a house, field, woods, a patient entrapment, etc. fast and unencumbered! Excellent Product! I also purchased the First Tactical IV, Med, Trauma and Airway kits and they are the best I’ve ever used (and I’ve tried just about every other major EMS manufacture’s various “kits” or “modules”). The four First Tactical kits fit perfectly into my “critical care bag” manufactured by another major EMS bag company (the only reason I didn’t purchase the First Tactical ALS bag/box is because I already invested a lot of money in my jump bag and critical care bag). Which also reminds me how reasonably priced First Tactical’s IV, Meds, Trauma, Airway and Oxygen kits are…and as I mentioned they are the best…the organization in each kit is excellent, they are not that large, yet can fit a lot of equipment thanks to the “book-style” design First Tactical used! Finding equipment is fast and easy using the four mentioned kits…and the Oxygen Kit is a perfect compliment to those four “book-style” kits! I’m applying for an EMS director position in a certain part of a certain state and if I get the job, all BLS and ALS vehicles will be using the four First Tactical kits that I mentioned and the O2 kit! Thank you First Tactical!