The tie rod should be so arranged with coupling boxes (see Part I.) or cottered joints that it can be altered in length in order to set up the roof when required.
In large roofs it is an advantage to arrange the tension rods in the same way, either with union screws - cottered joints - or with reverse screws at either end, so that by revolving the rod the screws turn opposite ways, and lengthen or shorten the rods.
These shackles, etc., are not shown in the small scale figures. They are often omitted in practice, the result being that the tension rods either become slack or undergo a greater stress than they are intended to bear.
Several forms shown in FiGs. 290, 291, 293, 294, 295, also in Fig. 296.
Plates V. VII. VIII. IX. X. XL XII. They require no explanation. Figs. 296, 297 show simple forms constructed with plates.
Suspending Rods for large roofs are similar in every respect to those described in Part I., and nothing more need be said regarding them.