Screwdrivers date back to the mid seventeenth century, when they were called “turnscrews”. (In modern French and Dutch they are still know as that, eg. Tournvis in French. In other modern European languages they are called the equivalent of unscrewers or screw-pullers.)
Types of Screwdriver Tip
- 1. Straight. The most commonly seen screwdriver is the kind with a flat tip intended to drive a screw with a slotted head. The tip is ground into a round or square shaft and usually tapered. It is also known as a cabinet tip screwdriver, for it’s predominate use in cabinet making. There is also a variation called a parallel tip that has a non-flared shaft end. It is useful for turning a screw which is at the bottom of a hole or in restricted areas and is used in electrical and electronic work.
2. Phillips head tip screwdrivers have an x-cross pattern formed by four fluted protuberances ground into the tip. The screw they are designed to drive has two crossed slots. They have an increased grip between the screw and tool, since there is more driving surface engaged. Phillips head screws are designed to cause the driver to toque out when overtightened, preventing overtorque of fasteners.
3. Posidriv head tips are similar to Phillips head tip. They have an additional feature of fitting into a square hole in the center of the crossed slots on the screw head. They are less prone to stripped heads.
4. Clutch head screws are used in frequently manufacturing products such as stoves, mobile homes and trailers. The screwdrivers are designed to fit into a butterfly shaped depression in the screw head.
5. Robertson head screwdrivers have a square tip with a slight taper, that fits into a square depression in the mating screw. Also known as a square drive screwdriver, it was invented by a Canadian in 1908. It allows for one-handed driving of screws, since the screw will usually not fall off the square tip once engaged.
6. Torx head screws have a six point star pattern, and they are accordingly also called star screws. The technical specification is ISO 10664. These screws are used in the automotive industry, in computers and hard drives and consumer electronics goods.
7. Hex head, or allen head screws, are similar to the Robertson square drive screws, except instead of a four sided hole, they have a six sided hole. The are sized in both metric and imperial denotations.
There are other types of screw driving systems, including tri-wing, spanner head, triple square, polydrive, spline drive, double hex and Bristol heads, but these are less commonly used.
Screwdriver Care and Maintenance
It’s important to select a screwdriver of the right size to fit in the screw head and that has a correctly ground driver tip. Chipped, rounded or undersize tips will slip and damage the screw head or surrounding area. But you also shouldn’t use one that is too big for the screw, especially on countersunk or counterbored screw holes. Don’t try to use a slotted tip screwdriver on a Phillips or allen head screw; this is a sure way to damage the screw head and once damaged, it will be difficult if not impossible to remove.
To repair a chipped straight tip screwdriver, grind each side of the tip with an oilstone, making sure to maintain the blade at the proper angle for it’s taper. Alternately, the blade tip can be reground on a power grinder with an emory wheel.
Photo by Andrew Turner, Creative Commons Attribution License