What is the difference between a Table Saw Splitter/Spreader and a Table Saw Riving Knife?

A Table Saw "Spreader"  (also commonly called a "splitter"), is mounted to the saw's rear trunion causing its height to be stationary. It tilts with the blade, but does not move up and down with the blade. It must be removed from the saw before making any non-through cuts (like a dado or groove - any cut that does NOT extend all the way through the workpiece). The spreader/splitter is located slightly behind the saw blade and is slightly thinner than a saw blade. As wood is cut, stresses in the wood can cause the saw kerf (the slot produced by the blade), to close-up behind the blade. The spreader/splitter prevents the wood from closing on the back edge of the blade (which if allowed to happen could cause kickback). The spreader/splitter has been a required "standard" safety item on table saws sold in the United States for many years.

A Table Saw "Riving Knife" serves the same purpose as a "spreader" (by preventing the cut wood from closing on the rear of the blade). The riving knife is mounted directly to the table saw's arbor bracket so that the riving knife tilts and also moves up and down with the blade. It is also typically fitted closer to the back edge of the blade than many spreaders.. The riving knife can remain in place during  non-through cuts using a standard blade, but must be removed when using dado or moulding heads. Different riving knifes are required for different style blades but they typically have some type of quick-release mechanism that makes them very easy to change. The riving knife has been a required "standard" item in Europe for many years.

Recent regulation changes have made the riving knife acceptable in the United States, therefore some new American table saw models including DeWALT models DW744 and DW745 now include a riving knife.