| 摘要 |
The brick, having parallel front (2) and rear faces, top (4) and bottom (5) edges and one or more cavities (C1), is made with projecting rectangular-section ribs (13, 14) along its lower edges. The ribs measure e.g. 15 mm wide by 2 mm deep and are set in from the front and rear faces by a few millimeters. They are made by applying a grooved rammer to the top of the mold in which the brick is made (upside down), and can be machined when set to reduce tolerances to under 0.5 mm.
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