The thread shown in the H table is the wood screw thread. It is standardized according to DIN 7998 and, as the name suggests, is intended for use with wood screws. The screws designed according to the specifications in the H thread table include half-round and countersunk wood screws with slotted or cross recess. Wood screws according to the H thread table are designed to be used in wood processing. The special feature of the thread from the H thread table is that in most cases there is no holding thread. The wood is simply pre-drilled and the H thread from the table then cuts the required internal thread into the material when it is screwed in. The geometry of the wood screws is also designed for this purpose and the H thread table also takes this into account.
The wood screw thread has a flank angle of 60°. The thread designation according to the H thread table is made up of the abbreviation H and a numerical value that reflects the outer diameter. The nominal dimensions in the H thread table range from 1.6 to 20 mm.
A minimum value for the outside diameter is also listed in the H thread table. In addition, the H thread table contains a metric value that specifies the required diameter of the core hole. With regard to the pitch, it is noticeable in the H thread table that a very high value is specified here - for example in comparison with the metric ISO thread. This is caused by the wide valleys that are clearly visible in the thread profile of a wood screw. According to DIN standard 7998, the pitch of the wood screw thread is also a value that may be subject to slight fluctuations. How large these fluctuations may be can also be determined using the H thread table. A separate column clarifies the permissible deviation of the pitch P in mm. These are always +/- values that fluctuate around the mean value P specified in the H thread table.