123A beef plate short ribs, trimmed originate from the mid-section of ribs 6 through 8. For barbecue, these would typically be referred to as “3-bone beef ribs” and the ribs are 8-12 inches long. Therefore, they may include some of the rib portion historically found in a whole primal rib as well as the portion of the rib found in the plate. The major muscle in 123A beef short ribs is the Serratus Ventralis muscle which may contain a great deal of marbling (deposits of fat within the muscle). The rib bones are typically wide and more oval shaped from this area of the beef carcass.
See more examples of the 123A Beef Plate, Short Ribs, Trimmed below: