Countersunk screws CR H ISO 7046-1-4.8 plain M3x20 mm

Steel is an iron-carbon alloy with a maximum carbon content of 2% by mass. The steels achieve their intended physical and mechanical properties through various hardening, annealing and tempering processes. It is also possible to harden the edge zone by surface hardening, case hardening or nitriding. Well-known steel grades are structural steels, free-machining steels, case-hardening steels, nitriding steels, tempering steels, tool steels and stainless steels.

The term plain indicates a completely untreated, merely oiled, smooth surface for all DIN and ISO screws such as wood screws, hexagon head screws, threaded rods, nuts and many types of washers.

Phillips (PH) screws, standardized in ISO 8764 (blades) and DIN 7962 (Phillips recess), are widely used. For screws with a Phillips cross slot, the flanks of the cross slots taper as the depth of the slot increases. With the PH system, threaded and self-tapping screws that are difficult to access can be tightened and loosened even from a slight acute angle to the screw axis.

The number before the point multiplied by one hundred gives the nominal value of the tensile strength in N/mm2, the number before the point multiplied by the number after the point and multiplied by 10 gives the nominal value of the lower yield strength in N/mm2. The number after the decimal point provides information about the yield strength, as a percentage of the tensile strength.