| In this double lock seam, the cleat is folded securely into the seam, as shown in. Fig. 29 (b), and holds the roofing to the boarding. This joint is more watertight than the single-lock standing-seam joint. These joints can be formed as shown, or the reverse. The fold in the latter case will be to the left. A detail of a double-lock s e a m, showing the progressive steps in forming it, is given in the upper right-hand corner in Fig. 21. |  |
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