Draft:Spax (screw)



Spax (stylized SPAX) is a registered trademark that was introduced in 1967 by the German screw manufacturer Altenloh, Brinck & Co (ABC) for a new type of self-tapping multi-material screw. The name Spax is an acronym for particle board (German: Spanplatte) screw with cross recess (×). Its geometry was an innovation for timber construction, as the particle board materials increasingly used in furniture and drywall construction since the 1950s cannot be securely installed with conventional wood screws, as these damage the panel structure when screwed in.

Design


Screws of this type differ from classic wood screws (for example, wood screws with hexagon or with slot) by a different ratio between outer and core diameter, that is, the core diameter is smaller here in proportion. This reduces the screw-in resistance on the one hand and increases the thread overlap from material to screw on the other. The shear resistance of the screwed material associated with this overlap increases the achievable pull-out strength. The threads are much sharper than those of other wood screws. In addition, the core is cylindrical, whereas in classic wood screws it is tapered.

A special feature of Spax screws is the corrugated thread in the first turns of the point, introduced in 1989. This reams the screw-in material and allows the subsequent thread to follow with less friction. The risk of the screw loosening under dynamic load is thus reduced. The corrugated thread and the position of the square thread tip at a special angle to the thread pitch contribute to the fact that the torque to be applied when screwing in is lower. Only a little material is displaced, which minimizes the risk of the workpiece tearing or splitting at the screw-in point.

Variants
Over time, Spax screws were developed not only for chipboard, but also for other materials, such as softwood, hardwood, plastic, plasterboard and sheet metal, and equipped with different screw heads depending on the application. The drive type was initially Phillips, later Pozidriv. In 2005, the company's own T-Star plus hexalobular socket screw drive was introduced, which has an additional recess in the screw head and a corresponding stubby tang on the bit. The Torx ttap power drive features an almost identical design.