Extracts from AmazingRibs here.

At the rear of the chuck, where it connects to the rib primal there are about two steaks called chuck eyes that are practically the same as the vaunted ribeye, only a lot cheaper.

Loin (Short Loin & Sirloin 17%)

Here’s a section that can challenge the rib primal for primacy when cooked properly. Again, the main muscle is the longissimus dorsi muscle. The longissimus has many popular names in the loin section: Strip steak, New York strip, Kansas City strip, shell steak, loin, and strip loin.

The other main muscle in this primal is the tenderloin, or psoas major. This is the muscle from which filet mignon and chateaubriand is cut.

Strip is marbled and mouth coating, tenderloin has little fat and is the most tender muscle on the steer. Delightfully, the two come together in T-bone and porterhouse steaks.

The T-bone and porterhouse are similar looking steaks with the two muscles separated by a T-shaped section of backbone. One side of the T has a large section of loin and the other has a small section of tenderloin. The difference between the porterhouse and T-bone is the size of tenderloin. Because the tenderloin tapers like a baseball bat and the T-bone is further to the front of the animal, the tenderloin portion is smaller than on the porterhouse, a minimum of 1/2″ wide at the T. The tenderloin on the porterhouse must be a minimum of 1 1/4″ wide, but they can be up to 3″ wide as you move to the rear.

Sometimes tenderloin/filets are left on the T-shaped bone, sometimes they are removed. Ditto for the loin. Interestingly, porterhouse is getting hard to find because the animals are getting so big that a 1″ steak can weigh a whopping 25 ounces.

Tri-tip is the poor man’s tenderloin, and strip loin roasts can be just as good as prime ribs.