Station Regulators are generally the same as Pipeline Regulators with one exception -- they have a "C" inlet nut and stem. A "C" nut (7/8"-14) is a little larger than a "B" nut (9/16"-18). If you are interested, there is also an "A" nut (3/8"-24) and a "D" nut (1 1/4"-12). They are made available mostly for Oxygen and Fuel gases (R&L) but they also have a system for inert gases too -- let’s ignore inert gases for now.
"B" fittings are what you commonly see on torches and regulators in the welding and cutting industry. "A" size can usually be found on small, light duty regulators and torches like those used by plumbers, artists, etc. As the demand for "volume" goes up, you'll see that the size of the fittings gets larger. They go to the "C" and "D" sizes. You'll generally find them on high flow regulators and very heavy cutting and heating equipment.
One real neat thing about all these hose connections, and they are commonly called "hose" connections, is that they come with a 200 psig maximum pressure limitation. This is a CGA "standard" and it should never be exceeded. Any time an "A", “B", "C" or "D" connection is used; you should never expose them to pressures greater than 200 psig.
The pressure limitation inherent with these hose connections is the main reason why they use a "C" connection on the inlet of a Station Regulator. It is to put a limit to the amount of pressure that will be going through it. A true Pipeline Regulator does not have this limit and, in essence, it can be run at pressures higher than 200 psig. The only limitation is on the design of the particular regulator itself. For example, you'll notice that our 447 and 547 pipeline regulators are limited to 400 and 500 psig respectively and our 2548 can safely be exposed to full cylinder pressures without incident.
The whole Pipeline/Station regulator thing originally came about because individuals were putting high pressure cylinder connections on the inlets of pipeline regulators and blowing themselves up. In 1985, CGA came up with the "Station" regulator concept to help prevent this situation.
Keep it Simple
So, to make it simple, a "Station” regulator is essentially a "Pipeline" regulator with a "C" hose connection installed to help prevent the possibility of someone using a regulator designed for low pressures (max 500 psig) on a high pressure source causing an incident and/or possible injury.