The USPS has new Tab (Wafer Seal) regulations for pieces that qualify for “Letter” rate in the Booklet style category. What defines a booklet from other “Letter” rate pieces is simply having staples/stitches in the piece’s bound edge or final fold (spine).
While holding the mail piece in front of you reading the mailing panel in the correct orientation, the spine can either be on the right side (leading edge) or bottom of the mail piece. Once you have established your spine you can now determine where to put your tabs!
The USPS requires Booklet style Letter rate mailings to use three non-perforated one and a half inch tabs to get a postage discount. The location of the spine will determine the placement of the tabs. If your piece has a spine on the leading edge then you will need to have two tabs on the top of the piece and one on the trailing edge (left side) in the middle (example B). If your spine is on the bottom then the requirement is to have two tabs on the leading edge and one on the trailing edge towards the top (example A).