500 Number 10 Single Window Envelopes – Thick Gummed Seal – Designed for Secure Perfect for mailing Invoices, QuickBooks Invoices and checks, billing statements, checks, and other business mail.No need for tape or glue sticks as our strong gummed seal creates a hassle free and safe seal for all your sensitive documents.Provides complete business mail security: your professional business mail will be completely hidden with our dark security tint designCreate professional looking mail with the added security of a single window envelope. Your business mail recipient address will show through the single window and you can quickly print your return address or add return address labels Shipping