This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The corner stones of a building are called quoins, and they are often given prominence over the face of the wall, as in Fig. 143. In broken ashlar the quoins should be as large in height as the largest of the wall stones. Stones at the sides of openings are called jamb stones and are often used in a manner similar to quoins. Lintels or caps are the stones which cover door 01 window openings. They are usually in one piece, as in Fig. 144 A, but are sometimes necessarily jointed. (Fig. 144 B.) In this case the joints should be "toggled" as shown. If the lintel spans an opening which is too great for its carrying capacity, it may be assisted by the use of a steel angle-bar or beam. (Fig. 145.) Lintels should bear at the ends at least four inches, and in the case of the lintel being thicker than the jamb, it should have bearing enough to reach beyond any recess which the window frame may require, as in Fig. 140, so that the inside of the lintel will be supported.