Each mail box is designated with an individual name tab for each slot. Use tab to organize materials by student, subject or class period. You can mix and match the three sizes to get the right number for your class size. The slot sizes for the 30 Slot Mail Box are 1 3/4"H x 10"W x 12 1/2"D. The slot sizes for the 10 and 15 Slot Mail Boxes are 3"H x 10"W x 12 1/2"D. Recycled and recyclable.