The fixed artillery used in fortresses up to the 19th century were usually ineffective in the lateral directional area, as the block mounts used up to then were not equipped for this. The lateral direction could only be done very imprecisely by lifting the entire carriage. To remedy this, the number of support points of the mount was reduced from four to three by placing it on a vertical bolt, the so-called pivot bolt, as a pivot point in the front area of the barrel and at the rear in the area of the breech or gun base under the Mount two transverse wheels attached. The bolt could be attached to the wall as a hook under the embrasure or anchored in the ground with the help of a reinforcement trestle or frame, then this bogie in its entirety was called a pivot.
Thanks to the two transverse wheels, it was now possible to achieve a side straightening range without great effort that was previously not possible. With casemated guns, depending on the nature of the embrasure, up to 45 ° to each side and, with guns set up in open bedding, up to 90 ° to each side, depending on the nature of the barbed ( gun bank ).
In addition, there were still center pivot mounts, here the pivot bolt was located centrally under the center of the gun platform, which thus rotated in its entirety around the pivot bolt. But this was only possible with guns that stood freely on the ramparts, i.e. H. were not housed in casemates, as the barrel muzzle with the entire gun was in a circular motion.
- Erwin Anton Grestenberger: Imperial and Royal fortifications in Tyrol and Carinthia 1860 - 1918 . Verlag Österreich ua, Vienna 2000, ISBN 3-7046-1558-7 .