Protect fragile mirrors, valuable artwork, or other flat and narrow items with this adjustable box. Each set can accommodate sizes up to 37″ x 61″. Inner box (inside) dimensions are approximately 37″ x 3″ x 27 1/2″. Outer box (inside) dimensions are approximately 37″ x 3 1/2″ x 30 1/2″. Full-overlap flaps (FOL) provides extra stacking strength and edge protection.