OEM Quality Park Redi-Seal Window Envelopes are designed for use with Insurance Form CMS-1500 and similar forms. These No. 10-1/2 envelopes feature a Redi-Seal closure that requires no moisture to seal; simply raise the lower flap and press to seal. The 1" x 4-1/2" window is positioned 4-1/4" from the left and 19/16" from the bottom of the envelope, ensuring easy visibility of your documents. With an inside security tint for added privacy, these envelopes are made from durable 24 lb paper.