#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 herkka 500 self seal double window security envelopes - designed for quickbooks checks - computer printed checks - 3 5/8 x 8 11/16 (not for invoices)