Columbian Business Envelopes, Gummed, 3 5/8 x 8 5/8 Inch, Double-Window, White, 500 Per Box (CO158) White window envelope with a 24-lb. paper stock features a moisture activated gummed closure; 3-5/8 x 8-5/8 inches; 500 per box Executive Style diagonal seam V-flap construction; security tinted for added privacy and confidentiality Double window allows the mailing and return address to show through; diagonal seams work well with insertion and extraction equipment; use for invoice processing