NOTICE: THESE No8 DOUBLE WINDOW ENVELOPES ARE NOT COMPATIBLE WITH QuickBooks INVOICES. #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.