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The surfaces of timbers need to be identified for precise descriptions of joints. For a horizontal rectangular timber (eg a wall plate), the surfaces are named top, soffit (bottom), together comprising the faces, and two sides. (The sides have hitherto generally been called edges, but this causes confusion with Edge in its common English meaning.) By convention, when a timber is set obliquely (eg a purlin), the surface facing towards the ridge becomes the top and the others are named in relation to this, including upper and lower sides. In a truss, the upper or fair face and lower face are labelled as if the truss was lying on the ground, the pegs being driven from the upper face.

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