| 摘要 |
A double-thread screw (1) for concrete comprises a hexagonal head (3) and a screw rod having, from the hexagonal head (3) toward a point (2), a metric screw thread (9), a smooth or not threaded portion (8), a self-threading portion (4) for concrete and a point (2). The self-threading portion (4) for concrete has two threads, i.e. a low thread (5) and a high thread (6), the high thread (6), as seen in a central longitudinal cross-section view thereof, having a side at an angle of 45 degrees and an opposite side at an angle of 10 degrees, with respect to a transversal axis of the screw. |
