Table 6-2.-Nominal and Dressed Sizes of Lumber
significant defects but no knotholes or other
serious defects. It must be suitable for use as
grain-tight lumber. No. 3 common contains a few
defects, larger and coarser than those in No. 2;
for example, occasional knotholes. No. 4 is low-
quality material, contains serious defects like
knotholes, checks, shakes, and decay. No. 5 com-
mon holds together only under ordinary handling.
STRUCTURAL LUMBER is graded accord-
ing to allowable stresses that determine its safe
No. 2 common contains a limited number of
load-carrying capacity. This capacity is based on
various factors, such as species of the wood,
density, moisture content, and other character-
istics that affect the strength of the lumber.
Factory and shop lumber is generally graded by
its intended use; the grades vary greatly from use
to use.
Board Measure
The basic unit of quantity for lumber is called
a BOARD FOOT. It is defined as the volume of
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