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SCREWS TYPES

If you thought there were only two types of screwdriver, flat (for slotted screw heads) and cross-head (for Phillips and Pozidriv) - think again! There are ten basic types of screw / screwdriver, and also a dozen different shapes of screw head.

A good place to see pictures and descriptions of each is Wikidpedia - and you will also find a summary of the various screw-size-classification systems (Whitworth, BA etc).

If you find the following article too 'basic' see the American engineering company Engineering Parts Sourcing Inc: screw point types, hole sizes, head types, screw thread data, metric conversions, screwdriver sizes, or for the geometry of the screw thread try Western Australia's School of Mechanical Engineering.

FLAT-HEAD

Flat screwdrivers (for slotted screw heads) are the most common of all, especially for spectacles and watches. We sell specialist small sets of screwdrivers for very tiny objects - if you want larger screwdrivers go to your local DIY store.

CROSS-HEAD

The Phillips screw has slightly rounded corners and is designed so that the screwdriver will slip out ("cam out") under turning-pressure ("torque"). This is to prevent over-tightening. So when customers complain that our screwdrivers are no good because they keep slipping out of the screw - they're meant to!

There are other varieties which do not cam out: the Reed and Prince and the Frearson have 'sharp' crosses and, similarly, the Pozidriv has four extra points which make it star-shaped. Another cross-shape that does not cam out is a BNAE, a tiny screwdriver-head in the form of a 'bit' for a power tool.

CLOCK AND WATCH KEYS (WINDERS) AND HEXAGONAL (HEX)

Old clocks and watches don't have inbuilt winders (they hadn't been invented) - you must wind these with a special square key, and these come in dozens of sizes. In the world of screws they are known as the Robertson design...but we don't actually sell the 'screwdrivers' because the 'screwdriver' (male) is fixed to the clock or watch, and it is the 'screw' (female) that is the winder. We sell these winders in all sizes, to fit the smallest watch and the largest longcase clock (used for winding up the pendulum).

The same principle (of 'winders' rather than 'screwdrivers') applies to meter cupboards and radiator taps, our Utility Key has two Robertson, one triangular and one round (all female) keys. We also have the traditional (mail) screwdriver in hexagonal ("hex"). A variation we don't sell (because you can get them in every DIY store) is the right-angle Robertson driver which are known as Allan keys.

Another variation is a very long blunt screwdriver in the form of a six-pointed star, known as the Torq, which also comes in a 5-pointed-star version (5-part) - these fit many mobile phones.


MOBILE PHONES AND OTHER MODERN ELECTRONIC DEVICES

The only thing that is special about mobile phones is that the manufacturers don't like you opening them, and so they use a variety of screws with obscure heads, on the basis that you will never find a screwdriver to fit. Our set of mobile phone screwdrivers have flat-head, spanner-head, tri-wing, Phillips, 5-part and Torx.