A saw blade is an integral part of many tools found in a wood or metal working shop.  Saw blades come in a variety of shapes and sizes and are not typically interchangeable.  One thing to keep in mind is the general difference between saw blades meant for wood and metal. 

A blade for wood generally has teeth that cut through the wood due to their sharpness.  On the other hand, a blade for metal typically does not have teeth: instead it has some sort of abrasive or grinding agent such as silicon carbide or diamond that grinds away the metal.  This also means that the two different kinds of blades generally age differently:  a wood saw blade will have teeth that get dull but generally the blade stays the same size.  A metal blade will actually become smaller over time as the blade gets worn down. 

Saw blades also come in different forms to match the cutting tools they work with.  A bandsaw uses a blade that is a continuous circle with a cutting surface on one edge.  A circular saw or chopsaw uses a circular blade.  A reciprocating saw uses a straight single blade.  When replacing the cutting blade on any of your tools, it’s critical to buy the right kind of blade.  The easy way is usually to find a blade from the same manufacturer which is almost guaranteed to work.  More generic blades are usually cheaper and probably work just as well in most cases, but you will need to be careful to buy the right style and size.  The manual that came with your tools can generally give you the specifications for the appropriate replacement saw blade.