OEM Quality Park Redi-Seal Single Window Envelopes come in a box of 500. These No. 10 envelopes feature a unique double-flap design that requires no moisture for sealing; simply raise the lower flap and press. The 1-1/8" x 4-1/2" window is strategically positioned 7/8" from the left and 1/2" from the bottom. Made from durable 24 lb. white wove stock, these envelopes are ideal for professional mailing needs.