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.