If the timbers are at right angles they are fixed as [fig. 98].
If both these joints occur the irons are placed as [fig. 99].
They should be fixed on both sides of the timbers joined.
Bolts.—Bolts ([fig. 100]) are of wrought iron, and their different parts should be in the following proportions:
| Thickness of nut | = | 1 diameter of bolt |
| Thickness of head | = | 3⁄4 diameter of bolt |
| Diameter of head or nut over sides | = | 13⁄4 diameter of bolt |
| Size of square washer for fir | = | 31⁄2 diameter of bolt |
| Size of square washer for oak | = | 21⁄2 diameter of bolt |
| Thickness of washer | = | 1⁄3 diameter of bolt |
There are disadvantages to the use of bolts in scaffolding. For instance, the beams are weakened by the cutting of the fibres; and, if the timber shrinks, the bolts may become loose. On the other hand, they can be easily tightened after the framing has settled into position.
Fig. 100
Their strength depends upon the quality of the iron, but varies between 20 and 25 tons of tensile strain per square inch of the smallest sectional area (Anderson).
Washers are used to prevent the nut sinking into the wood when tightened, and are equally necessary, but not always seen, under the head. They should not be cut into the under side of timbers subjected to a cross strain, as the cutting of any fibres is a source of weakness. Bolts are used where dogs and spikes are of insufficient length or holding power.