The height of the arch varies slightly, inasmuch as the inner curve may be about a diameter from the architrave, but in the Corinthian order should not fall below the level of the necking moulding of the capital. _The Baluster_ As already stated, the pedestal may be used as a part of a balustrading associated with balusters, and must conform to the proportions necessitated by the conditions. The usual height for balustradings, whether to steps, balconies, or before windows, is three feet two inches, though in special cases it may be slightly more. The baluster is a species of small column. Its usual form is bulbous or vase-shaped, and it is furnished with a capital and base. A series of balusters is technically known as a balustrade. The balusters are raised on a plinth, which corresponds to the plinth of the pedestal, and surmounted by a rail of horizontal mouldings, which correspond to the capping of the pedestal; hence the baluster is of the same height as the die. The height of the baluster should be divided into five, then one-fifth will be the height of the base, and the capital exclusive of the necking will be another fifth. The extreme diameter of the bulbous shaft is one-third the total height of the baluster, and the diameter of the necking and the top of the shaft is about one-sixth. The capital has a square abacus slightly less in width than the plinth of the base. Below the abacus is [Illustration: No. 170. Detail of Balusters.] an ovolo and fillet, which are circular on plan. The necking is separated from the shaft by a small torus and fillet. The base has for its lowest member a square plinth, which occupies rather less than half the height and is equal in width to the extreme diameter of the bulbous shaft. Above the plinth is a scotia and a necking moulding, which are circular on plan. _Spacing of Balusters_ The balusters should be spaced with not more than half their diameters or less than a third between their bases, except when employed on the rake of steps, when they may be slightly closer. _Balustrading_ In a balustrading an unequal number of balusters should always be used, and not less than five in one group exclusive of the half balusters which are attached to the flanking or dividing dies. Seven and nine form very satisfactory groups, but if more than nine are necessary for the space to be filled, intermediate dies must be interposed, and these may vary from two-thirds to three-quarters the width of the principal dies. In some cases, when a large number of balusters are to be grouped, the dies are flanked by half dies, which are less in projection than the dies themselves.