A screw drive is a system used to turn a screw. At a minimum, it is a set of shaped cavities and protrusions on the screw head that allows torque to be applied to it. Usually, it also involves a mating tool, such as a screwdriver, what is a slotted screwdriver is used to turn it.
The following heads are categorized based on commonality, with some of the less-common drives being classified as “tamper-resistant”. These sizes do not necessarily describe a particular dimension of the drive shape, but are often arbitrary designations in the same sense as a “Size 8” dress. The slot screw drive has a single slot in the fastener head and is driven by a “common blade” or flat-bladed screwdriver. It was the first type of screw drive to be developed, and for centuries it was the simplest and cheapest to make.
The slotted screw is common in simple woodworking applications, but is not often seen in applications where a power tool would be used because a power driver tends to slip out of the head, potentially damaging the surrounding material. The sole advantage is that they provide some measure of redundancy: should one slot be deformed in service, the second may still be used.
Other names for these types of drives are cross recessed, cross-head, cross tip, and cross-point. A double slotted screw drive is not considered cruciform because the shape is not recessed, and consists only of two superimposed simple milled slots.
Thompson, who after failing to interest manufacturers, sold his design to businessman Henry F. The original patent expired in 1966, but the Phillips Screw Company continued to develop improved designs.
1930s dismissed the Phillips concept because it called for a relatively complex recessed socket shape in the head of the screw — as distinct from the simple milled slot of a slotted type screw. Pozidriv section below for details.
The design is often criticized for its tendency to cam out at lower torque levels than other “cross head” designs. There has long been a popular belief that this was actually a deliberate feature of the design, for the purpose of assembling aluminum aircraft without overtightening the fasteners.