This is the Traditional Scale of Hardness Collection and a Test Kit. Includes Streak Plate, Penny, Glass Plates, Nail and nine specimens 1" x 1.5" number coded. Grades 6-12. Ages 11-18. This is the Traditional Scale of Hardness Collection and a Test Kit. Includes Streak Plate, Penny, Glass Plates, Nail and nine specimens 1" x 1.5" number coded. Grades 6-12. Ages 11-18.