Notched corners for quick organization. Large, easy to handle 6-1/4" x 3-1/4" cards. Bold, heavy type to use with large groups. Durable, thick card stock (14 pt.). Self-checking. Great for small groups, pairs, and whole class participation. Great for teaching the relationship between +/-, (e.g.: 3+1=4 on one side, 4-1=3 on the reverse). Sold as a pack of 3 sets of flash cards.