500#8 Double Window Security 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 – Black. NOTICE: THESE No8 DOUBLE WINDOW ENVELOPES ARE NOT COMPATIBLE WITH QuickBooks INVOICES.