Country Style ribs are not really “ribs”. They’re a Boston Butt (shoulder roast) that has been cut into pieces.
Ribs extend from the backbone all the way down and around the animal to the underside where they are connected together by the sternum and Costal Cartilage.
Baby Back ribs, or Loin Back ribs, are ribs cut from near the backbone. These are located just under the loin and are very tender.
Spare Ribs are what’s left of the rib cage after the top part, the Loin Back ribs, have been cut off. The meat here is flavorful, but not as tender.
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Typically, Loin Back ribs are smoked or grilled. Country Style ribs are braised (and sometimes smoked). Country Style ribs can be tough if cooked too quickly, so braising is usually the preferred method.
They really aren’t very interchangeable.