#6 3/4 Reply Business Envelopes Envelopes - 50 Per Pack (Pastel Blue) #6  BlankReply Business Envelopes envelopes are used by most businesses as a return envelope as it fits great when inserted in the #9 and #10 Standard Envelope (#6-3/4) 3-5/8" x 6-1/2" Moisture activated gummed seal. Our 6 3/4 envelope is the envelope to use when you want your mailing to make a splash 50 Envelopes per pack By using colored envelopes a business would be able to take their mailings and letters to the next step.