HCFA Envelopes W2A38821C, Window Style, 4-1/2 x 9-1/2", Gummed Flaps ( Moistening Required), Box of 100. No. 10 1/2 envelopes are designed for use with Insurance Form CMS-1500 and similar forms. The 1-1/8" x 4-3/4" window positioned 3-7/8" from the left and 1-1/2" from the bottom of the envelope. Inside security tint offers more privacy. 24 lb