Quality Park Products Products - Security Window Envelopes, 24Lb, 4-1/8"x9-1/2", 500/BX, WE - Sold as 1 BX - Security Window Envelopes require no moisture to seal. Raise the lower flap and press. The unique double-flap design keeps gum from sticking until the envelope is ready to mail. Inside tint for privacy. Window (1-1/8" x 4-1/2") is positioned 7/8" from left and 1/2" from bottom. Self-sealing No. 10 envelopes are made of a white wove material. 24 lb.