Saddle Stitching is a book binding method in which the pages of a book are collated, folded, and stapled in the center of the book. Most books can be saddle stitched on an automated saddle stitching machine, but some specialty saddle stitched books like books with shingled or stair stepped pages, must be stitched using a manually fed machine.
I guess we call it saddle stitching instead of saddle stapling because our "stitches" come from snitches, no not really, they come on a long spool of wire instead of pre-formed staples like you might find in your Swingline. Commercial Printers like Voom have machines that form the staples as we are making the books, so they can be set to the exact right length for your book thickness.
When creating a saddle stitched book, your page count must be in 4 page increments, since each folded piece of paper is going to be 4 pages in your finished book.
When referring to the size of a saddle stitched book, it is important to note the direction - an 8.5 x 11 book is a book that will be 11 x 17 when you open it, if you say you want a 11 x 8.5 book, it will be 22 x 8.5" when you open it up - not every printer can make landscape format books that are 11 x 8.5, but Voom can!
Our minimum stitched book size for our automated saddle stitcher is 4.7 x 3.5" and our maximum finished book size is 14 x 12" and we can stitch books up to .15" thick and up to 80 pages - thicker than that, we can either manually stitch, or we look at perfect binding or coil & wire binding options.