Hcfa Envelopes, Window Style, Size: 10-1/2 (4-1/2 X 9-1/2"), Self Seal Flaps (No Moistening Required), Box of 500 HCFA, CMS-1500 Health Insurance Claim Form Window Envelopes. Box of 500 envelopes. Self Seal flaps - No Moistening Required. Size: 10-1/2 ( 4-1/2 x 9-1/2"). 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. 92 Brite.