Sentence:  Whereas if the Header of one side of the wall, <WSD>toothed</WSD> as much as the Stretcher on the other side, it would be a stronger Toothing, and the joints of the Header on one side, would be in the middle of the Headers of the course they lie upon of the other side 
Meaning of the word marked with <WSD> tags:  To lock into each other, like gear wheels.