Countersunk chipboard screws Pozi partially threaded steel zinc plated blue 4x30

A further development of Form H are Pozidriv (PZ) screws, standardized in ISO 8764 (blades) and DIN 7962 (Phillips). With the Pozidriv screws, the flanks of the screw head run parallel to each other in the depth of the screw head. Due to the more precise fit, the direction of force is precisely determined and higher torques are possible because the cam-out effect is prevented.

Case hardening is used to impart significantly greater hardness to the surface layer of steel workpieces and to improve their mechanical properties. Case-hardened workpieces are characterised by increased wear resistance, a tough core and improved fatigue strength.

Blue galvanised finishes are produced either by electroplating in accordance with DIN EN ISO 4042 or by mechanical plating in accordance with DIN EN ISO 12683. For fasteners with a hardness exceeding 390 HV, there is a risk of hydrogen embrittlement during galvanising (electrolytic process). This necessitates specific measures (such as annealing), although these do not provide a 100 per cent guarantee against embrittlement.