Don't run out of CO2 in the middle of a job. Get the four pack and save $$. The 1.25# (20 oz.) bottle features a high end on/off valve instead of the cheaper "pin valve". This allows you to turn the pressure off even with your Sidearm regulator still attached to the bottle and keeps air from leaking out between uses. Note: This bottle has a manual on/off valve and not a pin valve. We recommend using a valve protector at all times as one drop without one WILL ruin the valve . All of our 20 oz. bottles come with a valve protector.