It is equal to the load at elastic limit (P_{1}) divided by the area under the plate (B).
{ P_{1} } { c = -- ----- } { B } SHEAR ALONG THE GRAIN _Apparatus_: An ordinary static testing machine and a special tool designed for producing single shear are required.

(See Figs.

36 and 37.) This shearing apparatus consists of a solid steel frame with set screws for clamping the block within it firmly in a vertical position.

In the centre of the frame is a vertical slot in which a square-edged steel plate slides freely.
When the testing block is in position, this plate impinges squarely along the upper surface of the tenon or lip, which, as vertical pressure is applied, shears off.
[Illustration: Fig.

36 .-- Vertical section of shearing tool.] [Illustration: FIG.