8D Nails (or smaller with a smaller blade)
A portable circular saw is great for ripping long, wide boards into narrow ones.
A portable circular saw is great for ripping long, wide boards into narrow ones. But as the saw moves along the board, the slot made by the blade -- called the saw kerf -- will often pinch closed and bind the blade in the cut. If enough pressure is exerted the saw will kick back and jump from the board.
To reduce the likelihood of kickbacks, slip an 8d (2 1/2-in.) nail into the kerf every 4 ft. or so. The nails will prevent the kerf from closing and pinching the blade. When cutting with a thin-kerf blade, switch to thinner 6d (2-in.) nails