Hcfa Envelopes, Window Style, Size: 10-1/2 (4-1/2 X 9-1/2″), pack of 100 HCFA, CMS-1500 Health Insurance Claim Form Window Envelopes. Pack of 100 envelopes. 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.