Concrete block units are made in sizes and shapes to fit different construction needs. Units are made in full- and half-length sizes, as shown

in figure 7-37. Concrete unit sizes are usually referred to by their nominal dimensions. A unit measuring 7 5/8 in. wide, 7 5/8 in. high, and 15 5/8 in. long is referred to as an 8- by 8- by 16-in. unit. When it is laid in a wall with 3/8-in. mortar joints, the unit will occupy a space 16 in. long and 8 in. high. Besides the basic 8- by 8- by 16-in. units, the illustration shows a smaller partition unit and other units that are used much as cut brick are in brick masonry.

The corner unit is laid at a corner or at some similar point where a smooth, rather than a recessed, end is required. The header unit is used in a backing course placed behind a brick face tier header course. Part of the block is cut away to admit the brick headers. The uses of the other shapes shown are self-evident. Besides the shapes shown in figure 7-37, a number of smaller shapes for various special purposes are available. Units may be cut to the desired shapes with a bolster or, more conveniently and accurately, with a power-driven masonry saw.

The sides and the recessed ends of a concrete block are called the SHELL (fig. 7-38). The

material that forms the partitions between the cores is called the WEB, and the holes between the webs are called CORES. Each of the long sides of a block is called a FACE SHELL, and each of the recessed ends is called an END SHELL. The vertical ends of the face shells, on either side of the end shells, are called the EDGES.