Assembly advice and instructions download service

home links about us supported by sparepartshelpline.com

Screwdrivers - what's the difference?

A screwdriver is a device specifically designed to insert and tighten, or to loosen and remove, screws. No surprises there!

There are many different types of screwdriver. For the purpose of the glossary, we will concentrate on the 5 most common types used in DIY and self assembly products. For screw head the most common are flathead, pozidriv, Philips cross head but hex (Allen key) and torx are becoming more common with regard to flatpack fixings.

Screwdriver - Flathead

A flat head is exactly as it sounds. The head is made of a single machined flat surface which is inserted into s slot in the screw head in order to turn it.

Screwdriver - Cross head/Philips

The Philips screwdriver and cross head screw came about due to automated production lines requiring the ability to have self-centring properties. Henry F. Phillips designed and patented the design but as it was copied so often he lost the patent.

Philips Screw Company and the American Screw Company went on to design the Pozidriv screw which can accommodate greater torque.

Screwdriver - Posidrive

The Posidrive is a type of screw head and screwdriver, this is slightly different to the classic cross-head Phillips.

They differ due to the way that they are machined. The Phillips driver has 4 basic slots cut out of it. For the Posidrive, each slot is the result of two machining processes at right angles. The result of this is that the arms of the cross are parallel sided in the case of Posidrive and tapered for the Phillips.

Posidrive is less likely to slip because of this, but as there are small protrusions left in the bottoms of the grooves, a posidrive driver will not fit a Phillips screw correctly.

A Posidrive-headed screw is easily distinguished from a Phillips by the small square recess at the crossing of the drive slots.

Screwdriver - Hex (Allen Key)

Hex screws and bolts have a hexagonal socket in the head. Using one size of hex socket on all of a products fixings allows a manufacturer to supply the correct tool for assembly at a very low cost.

Some hex keys have a ball on one end. This allows the key to be used at an angle off-axis to the screw or bolt.

Always use a corretly sized key for the socket otherwise you may damage the key or round off the socket leaving the fixing (bolt or screw) useless.

Screwdriver - Torx (aka Star)

Philips and Pozidriv screw heads were designed so that when too much torque was used the screw driver head would lift out of the socket to prevent overtightening. This is known as to "cam-out" With the advent of drivers that could consistently achieved exact torque, this feature was no longer needed.

Textron Fastening Systems developed Torx which was designed to prevent cam-out and allow precise torque to be used.