Flutes are small grooves cut into dowels. The flutes allow glue to travel down the dowel as it is inserted into the dowel hole. If a dowel is too tight, it will build up an hydraulic effect, and the dowel will resist penetration or stop completely as the glue seals off the hole, trapping pressure. Flutes relieve the pressure, allowing a dowel pin to seat completely into the dowel hole when the glue seeps through the flutes. If your dowel pins do not have flutes, you can cut some with a utility knife.
Mark and cut off 3-inch sections of the dowel rod with a hacksaw depending on how many you need. Lightly sand the ends of the 3-inch sections by hand with 100-grit sandpaper.
Hold one of the dowel sections flat against a work table between your thumb and your index finger. Grasp a utility knife like a pencil in the other hand.
Place the tip of the utility knife against one end of the dowel. Push down gently and drag the tip of the knife down the dowel, cutting to a depth of 1/32 inch. Repeat the cut, pushing harder this time to cut to a depth of 1/16 inch. It's OK if the cut is not perfectly straight, or if it does not run completely from end to end.
Rotate the dowel slightly and make another cut parallel with the first cut, 1/16 inch from the first cut.
Rotate the dowel again and make another cut 1/16 inch from the second cut. Continue rotating and cutting flutes into the dowel until you have cuts all around the dowel.
Be careful that the dowel doesn't spin in your fingers while you are cutting. Grasp the knife firmly so it doesn't slip. Always wear safety glasses when working with wood.