The sawbuck usually has two girths (double rigged). There are two basic types of sawbuck trees: "Tehama" which is wider and fits mules and quarter-type horses the best, and the "Humane" which fits slimmer horses. A sawbuck saddle is less expensive, lighter and a bit more stable on the animal's back because of the double rigging. It does not have the wide range of adjustment found on the Decker since there is no adjustment on the placement of the rigging rings nor on the angle of the bars of the saddle.
The Decker has a padded cover (called a half-breed) that is placed over the D's of the tree. Near the bottom of the half-breed there is usually a l' x 4" board that helps to spread the load on the side of the animal. Usually single rigged, the latigo passes over the side board in cinching the single girth around the animal. The rigging ring may be moved forward or backward on the animal, and the D's may be heated and bent to achieve the optimum fit of the wooden bars to the backs of individual animals, The Decker is usually heavier, and more expensive than a sawbuck.
The appendix lists books that are good sources for additional information on how to select the right packsaddle for your use.