A normal Forstner bit is 3-½ inches long. Certainly, the 1-1/8 inch long x 3/8 inch shank is chucked and deducted from the entire length, leaving around 2-3/8 inches of drilling depth available. A Forstner bit measuring 2-3/8 inches can drill a hole of 4-3/4 inches entirely through. After drilling to full depth, another one inch can be drilled with the same bit by extending the shank a half-inch out of the chuck. But do this slowly. Avoid doing this before boring to the maximum depth, otherwise, the Forstner's shank will spin in the chuck.