page_title: Screwdriver
section_title: Drive types
hierarchical_section_title: Screwdriver / Drive tip / Drive types
caption_attribution_description: I am the author of this image and I hereby release it into the public domain. It is a close up shot of the various sizes of Robertson head screwdrivers and their colour coding. Matt Deres 22:25, 3 December 2006 (UTC)
context_page_description: A screwdriver is a tool, manual or powered, used for screwing and unscrewing screws. A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. This form of screwdriver has been replaced in many workplaces and homes with a more modern and versatile tool, a Power Drill, because they are quicker easier and can drill holes too. The shaft is usually made of tough steel to resist bending or twisting. The tip may be hardened to resist wear, treated with a dark tip coating for improved visual contrast between tip and screw—or ridged or treated for additional 'grip'. Handles are typically wood, metal, or plastic and usually hexagonal, square, or oval in cross-section to improve grip and prevent the tool from rolling when set down. Some manual screwdrivers have interchangeable tips that fit into a socket on the end of the shaft and are held in mechanically or magnetically. These often have a hollow handle that contains various types and sizes of tips, and a reversible ratchet action that allows multiple full turns without repositioning the tip or the user's hand.
context_section_description: The tool used to drive a slotted screw head is called a standard, common blade, flat-blade, slot-head, straight, flat, flat-tip, or "flat-head" screwdriver. This last usage can be confusing, because the term flat-head also describes a screw with a flat top, designed to install in a countersunk hole. Furthermore, the term implies that a screwdriver has a "head"; it does not. Such a flat-headed screw may have a slotted, cross, square recessed, or combination head. Before the development of the newer bit types, the flat-blade was called the "Common-Blade", because it was the most common one. Depending on the application, the name of this screwdriver may differ. Within the automotive/heavy electric industries, it is known as a "flat head screwdriver"; within the avionics and mining industries, it is known as a "standard screwdriver". Though there are many names, the original device from 1908 was known as a "flat-head screw turner".
  Among slotted screwdrivers, variations at the blade or bit end involve the profile of the blade as viewed face-on (from the side of the tool).  The more common type is sometimes called keystone, where the blade profile is slightly flared before tapering off at the end, which provides extra stiffness to the workface and makes it capable of withstanding more torque.  To maximize access in space-restricted applications, the cabinet variant screwdriver blade sides are straight and parallel, reaching the end of the blade at a right angle. This design is also frequently used in jeweler's screwdrivers.
  Many textbooks and vocational schools instruct mechanics to grind down the tip of the blade, which, due to the taper, increases its thickness and consequently allows more precise engagement with the slot in the screw. This approach creates a set of graduated slotted screwdrivers that fit a particular screw for a tighter engagement and reduce screw head deformation.  However, many better-quality screwdriver blades are already induction-hardened (surface heat-treated), and tip grinding after manufacture compromises their durability. Thus, it is best to select a tip made to fit precisely to begin with, and avoid weakening the factory heat-treatment.
  Phillips screwdrivers come in several standard sizes, ranging from tiny "jeweler's" to those used for automobile frame assembly—or #000 to #4 respectively. This size number is usually stamped onto the shank (shaft) or handle for identification.  Each bit size fits a range of screw sizes, more or less well. Each Phillips screwdriver size also has a related shank diameter.  The driver has a 57° point and tapered, unsharp (rounded) flutes.  The #1 and smaller bits come to a blunt point, but the #2 and above have no point, but rather a nearly squared-off tip, making each size incompatible with the other.
  The design is often criticized for its tendency to cam out at lower torque levels than other "cross head" designs, an effect caused by the tapered profile of the flutes which makes them easier to insert into the screw than other similar styles. There has long been a popular belief that this was actually a deliberate feature of the design. Evidence is lacking for this specific narrative and the feature is not mentioned in the original patents. However, a subsequent refinement to the original design described in US Patent #2,474,994 describes this feature.
  Robertson, also known as a square, or Scrulox  screw drive has a square-shaped socket in the screw head and a square protrusion on the tool. Both the tool and the socket have a taper, which makes inserting the tool easier, and also tends to help keep the screw on the tool tip without the user needing to hold it there. (The taper's earliest reason for being was to make the manufacture of the screws practical using cold forming of the heads, but its other advantages helped popularize the drive.) Robertson screws are commonplace in Canada, though they have been used elsewhere, and have become much more common in other countries in recent decades. Robertson screwdrivers are easy to use one-handed, because the tapered sock
caption: A variety of Robertson sizes
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