The right bit for the right job
For the right bit, it`s not only necessary to match the screw, but also to stand the stress. The range of bits offered on the market, which seems to be confusing for amateurs, is due to the many improvements by screw and bit manufacturers, who constantly develop their products, and therefore offer many different bit versions.
The slotted screw was the first screw on the market and is still used today. The disadvantage of this head shape is that the bit can easily slip through, which might damage the screw. Also when the screw is turned quickly, the bit may slip off. This screw head shape is mainly used for manual screwing.
Phillips screw (Phillips, PH)
To improve slotted screws, a second slot was added to the screw head, and in order to provide more contact surface the centre was widened as well. This head shape prevailed for a long time. The bit cannot move outside, but if the contact pressure is not strong enough, it might slip and oscillate, which could also damage screw and bit.
Pozidriv screw (PZ)
The Pozidriv screw is an improvement of the Phillips screw, as it provides not only a cross-head but also additional notches. The bit provides edges that grip into the notches. This design protects the bit from slipping through.
The advantage of Torx screws is the extended grip surface for the bit. Instead of two slots, as on a Phillips screw, the Torx screw has three slots shaped like a hexagon head. The rounded edges help prevent material fatigue.
The Allen screw can also be considered an improvement of the Phillips screw. Like the Torx screw, the Allen screw also provides an extended grip surface, and it is very robust. However, this screw is not suitable for fast-turning machines, but is more widely used for manual screwing, especially in the metalworking field.
Some manufacturers develop specific headshapes for their screws. Other developments include Torx Plus screws, Tri-wing screws, square-head screws and other newly developed shapes that are only used for specific applications (for example in the field of automotive, electrical, and safety engineering).
Bit sets (standard quality)
Basically, the bit material must satisfy two requirements: it must be hard and tough.
However, because these are contrasting properties, the choice of material is crucial. For standard-quality bits, a tough steel is used that doesn't break easily and still has good hardening properties.
Bit set (torsion development)
The harder the bit, the longer its edge life, but with the disadvantage that the bit becomes brittle and breaks easily. In the development of these torsion bits, different applications (wood/metal) were analysed and the corresponding torsion forces determined. Based on the findings, a steel was chosen that is optimally tough for the given application but still very hard.