Dog Irons.—Dog irons ([fig. 96]) are bars of flat or round wrought iron, turned up at the ends, which are pointed. If both ends point in the same plane they are termed ‘male,’ if otherwise ‘female.’ The shank is about 12 inches long. Besides holding the timbers together, they exert a certain power of compression upon the joint they enclose. This is gained by hammering the inside of the spikes to a splay, leaving the outside to form a right angle with the shank.
Fig. 96
Fig. 97
Fig. 98
Fig. 99
They may be described as inferior straps, and their holding power is from 600 to 900 lbs. per inch in length of spikes, as deduced from experiments by Captain Fraser, R.E. Dog irons have the advantage that their use does not injure the timber to any extent, and so depreciate its value. Dogs are fixed according to the joint to be enclosed. If the joint is at right angles to the run of the timbers, they are fixed as [fig. 97].