11 1/4" x 8 3/4" x 12" 275# Heavy-Duty Corrugated Boxes. These cartons were designed to fit the most popular paper sizes. Prevent damage to forms, catalogs, letterhead and other printed material by using the right size carton. Heavy-Duty construction provides greater protection and stacking strength. Manufactured from Heavy-Duty 275#/ECT-44 singlewall kraft corrugated. These cartons are 40% stronger than standard shipping containers. Sold and shipped flat in bundle quantities. 25/Bundle.