Originally Posted by
Howard Acheson
If you bought the type of "stiffeners" that come as a pair, you MUST use both parts. They are designed generally with a raised ring around the perimeter of one side. These raised areas grip the blade equally on both sides of the blade exerting equal force in the same part of the blade plate. If you don't use one of the stiffeners, you may exert force in diffeerent parts of the blade causing the blade to have slight cone shape. This is very bad for the blade and even worse for the quality of the saw cut.
The Forrest "stiffener" is only a flat plate where the whole plate rests against the blade plate. It's intent is to add spinning mass which, in theory, results in a better cut. Because it's a flat plate, it can be mounted singly on only one side of the blade.
So, in summary, if the "stiffeners" you have comes as a pair, you MUST use both. If the "stiffener" is a single plate, then you only need one. The ones that come as a pair will move the kerf necessitating changing your rip scale and making new zero clearence inserts.