OEM Quality Park HFCA-1500 envelopes are designed specifically for use with Insurance Form CMS-1500 and similar forms. The window positioning allows the address on the form to show through without the need for folding. Featuring a Redi-Seal closure, these envelopes require no moisture; simply raise the lower flap and press to seal. The interior is tinted for privacy, and the window size measures 1" x 4-1/2", positioned 4" from the left and 10" from the bottom. Each envelope is made from durable 28 lb paper.