Ring

Ring is a circular course forming an arch. An arch might be made of one ring or more than one ring.

Impost

Impost is the projecting course at the upper part of a pier or abutment to stress the springing line.

Bed Joints

These are the joints among the voussoirs that radiate from the centre.

Centre or Striking Point

This is the geometrical centre point from while the arcs creating the extrados, arch rings and intrados are described or struck.