Quality Park No. 10 Single Window Security Tint Treated Business Envelopes - Business - #10 - 4 1/8" Width x 9 1/2" Length - 24 lb - Flap - White - 500 / Box No. 10 Single Window Security Tinted Business Envelopes are made with a material that inhibits the growth of mold and mildew to protect your contents. They produce dependable performance, providing quality, professionalism and convenience that meet your needs. Redi-Strip closure creates a secure seal. Simply peel off the strip and press to seal. 24 lb. bright-white stock gives mailings a professional look.