6 3/4 Envelopes-Regular Envelopes Color Blue-55 Pack 24Lb (Blue) These are standard 24 lb. blue stock with Moisture activated gummed seal and measures (3 5/8" x 6 1/2"). #6  Blank Regular envelopes are used by most businesses as a return envelope as it fits great when inserted in the #9 and #10 Standard Envelope! Colored, and customized, envelopes not only can help to set you apart from the crowd of other mail but it could possibly bring in more customers as well comes 55 in a pack