Measure the diameter of your dust collection port with a tape measure. For example, on the Powermatic 10-inch table saw, the dust collection port is four inches in diameter.
Measure the diameter of your Shop-Vac hose. Depending on the size of your Shop-Vac, the hose is 2-1/2-inches in diameter, 1-1/2-inches in diameter or 1-1/4-inches in diameter.
Select a dust collection reducer that measures the diameter of your dust collection port on one end and that measures the diameter of your Shop-Vac hose on the other.
Slide the larger end of the reducer onto the dust collection port on your table saw and then slide the hose of the Shop Vac vacuum onto the other end of the reducer.
Turn the Shop-Vac on before you start the table saw. As you rip the board on the table saw, the dust will suck into the Shop-Vac.