Book Band Pen Case in Black (B6-A5) by MidoriBook Band Pen Case by Midori. This Book Band Pen Case in Black from Midori lets you carry up to 4 pens inside it's slim design. It features an adjustable elastic strap to adjust the length making it perfect for notebooks ranging in size from B6 to A5. The pen case is made from a mix of materials including cotton and polyester that combines texture and durability. You can put your pens and pencils in the zipper pouch, of alternatively the pen pocket