Secondary regulators do not attach directly to CO2 tanks. They are designed to be used inline when you already have a dual gauge CO2 regulator. A secondary regulator allows you run multiple pressures from one tank of gas. CO2 line from your existing system would attach to secondary. Gas lines coming from the secondary can then be adjusted to different pressures (Pressure coming out of secondary can never be greater than what is coming in). Applications would include situations where you want different levels of carbonation in different beers or you want to run soda at a higher pressure than your beers. All secondaries have wall brackets for mounting. This is to go in line via flexible tubing, not to hard mount on to an existing regulator. Secondary regulators can be ganged (attached) together.