u00d7 1 2 inch long wood screw 12 fig1 illustrates a structural element retainer 8 attached to a plywood structural element through a 1 inch long u00d7 1 4 inch diameter bolt 13 and and nut 14 the bolt 13 is inserted into a 5 16 inch diameter hole drilled into the structural element the head of the bolt sets in a cavity formed by boring a 1 2 inch diameter hole a depth of 3 16 inch on the opposite side of the plywood from the retainer element 8 in all the above mentioned structural element attachment methods the centerline of the attachment bolts or fasteners are located on the structural elements a distance of 3 inches from the top 3 inches from the bottom and 5 inches in from each end as illustrated in fig1 in corner construction the centerline of the fastening rod conduits 7 are located 6 inches in from each end of the structural elements and on the longer leg of the corner block a third conduit 7 is located on a centerline 18 inches inward from the end of the longer structural element fig1 and 18 illustrate a block with an electrical box 16 assembled into the block a plastic or metal electrical wiring.