#8 Double Window Security Check Envelopes, No.8 Double Window Bussiness Envelopes Designed for QuickBooks Checks – Computer Printed Checks – 3 5/8 X 8 11/16 (NOT for INVOICES) – 24 LB – 500 Count. PREMIUM SECURITY CHECK TINT ENVELOPES: The interior of our No8 Security envelopes use a dark navy, heavy coverage security tint to the protection contents and sensitive information, a security tint makes envelopes hard to see through that ensures upmost privacy.