Building a masterpiece at your place? A bookcase, shelf or mantel for the fireplace? Here's how to choose the right lumber — by grade, type and number. For projects that will be in sight and visible — such as a bookcase or a shelf — choose clear or select grade lumber. That is to say, lumber with very few knot holes, little or no discolorations and no other defects. For utility projects, such as fences or things that will be painted, choose common grade wood. Remember that boards are nominally sized, meaning they aren't really what they're called. A 2 by 4 is actually 1-1/2 by 3-1/2 - strange, but true.And plywood comes in grades A through D. with A being the best. Grades tell you how many knot holes have been filled in the plywood. And, there's an N grade with facing that has none. Thus, with both plywood and lumber, the choice is clear (or select) or A through D.