The angle, measured from the horizontal, at which the outer bricks of a Flat Arch rest on the support brickwork
Lowest block of an arch, its underside is the springing (c/f).
The surface on which the arch joins the supporting abutment.
The inclined surface on which the arch joins the supporting wall. For jack arches the skewback is indicated by a horizontal dimension.
Slanting surface that supports either end of a segmental arch.