Columbian #10 Business Envelopes are a great all-purpose solution for mailing letter-sized business documents, especially invoices, statements, and checks generated through QuickBooks and similar accounting software. Designed for everyday office use, these double window envelopes allow recipient and return addresses to align perfectly and show through cleanly, eliminating the need for manual addressing or labels. Measuring 4-1/8"" x 9-1/2"", they comfortably fit standard 8-1/2"" x 11"" sheets folded into thirds for efficient, professional mailings. Each self seal envelope is made from durable 24 lb white wove paper, offering a professional look that reflects well on businesses and schools. A blue security tint with an interior safety pattern helps block visibility through the paper, protecting sensitive information from being read during handling or delivery. The double window design is aligned for QuickBooks and other computer-generated documents, allowing recipient and return addresses to display cleanly while keeping financial details private. The peel-and-press adhesive strip creates a strong, reliable seal without moisture, helping keep hands, desks, and mailroom workflows clean and efficient. Packaged with 500 envelopes per box, Columbian #10 Self Seal Envelopes are a dependable, never-out essential for offices, small businesses, and households that value security, convenience, and organization in their daily mailing tasks. (Manufacturer Item Number: COLO338)