Whenever you make a case, box, briefcase, piece of luggage, etc that's made from leather & requires stitching, we use a particular type of stitch called (you guessed it) a "box" stitch. Whenever two pieces of leather meet to form a corner in a case, there are a couple of ways to do this.
The first way to join two pieces of leather in a case together is called a butted joint. This is where the leather of one piece simply butts up against another. Almost every reel case you'll ever see uses this method: