Three-inch seal protects stored files from dust and dirt and ensures a flat top for stable stacking. Maximum security design with string and button closure keeps contents secure, even if box is overturned. Up to 50% stronger than other string and button boxes for stacking without shelving. FastFold quick and easy assembly. Reinforced, plastic handle makes it easy to pull a box out of a stack or off shelving. Ensures flat top for stable stacking.