Samac: Five Facts About the Humble Screw

Samac: Five Facts About the Humble Screw

Samac suggests five things you might not have known about screws

Screws may be small, but they are important – as anyone who has had one fail on them will testify! And there’s more engineering in a screw than you might imagine. Samac specialises in screws, nails and fixings so the company knows a thing or two about the humble screw. Here are five things you may not know about the screw.

1. What came first? The screw or the screwdriver? The screw predates the screwdriver, as the earliest screws were probably tightened with a knife. The flat head or slotted screwdriver was the first known head for a screwdriver until the early 1900s when a man named Phillips pioneered the cross head screwdriver that we are familiar with today.

Our Performance Plus screws now feature a Pozi head, an improved version of the Phillips screw, which is less likely to cam out and allows greater torque to be applied. The Pozidrive screws are distinguishable from Phillips by a set of radial indentations (or “tick marks”) set at 45° from the main cross recess on the head of the screw.

Make sure that you use the correct screwdriver for the screw head: using a Phillips screwdriver bit on a Pozi screw may damage the screw head. A Phillips driver has an angle on the flanks, a pointed tip and rounded corners. The Pozidrive screwdrivers have straight sided flanks, a blunt tip and additional smaller ribs at 45° to the main slots.

2. Going round in circles. The threading on a screw forms the shape of a helix, not a spiral. In his book One Good Turn: A Natural History of the Screwdriver and the Screw (what do you mean you haven’t read it?) Witold Rybczynski writes: “A spiral is a curve that winds around a fixed point with a continuously increasing radius. A helix is a three-dimensional curve that twists around a cylinder at a constant inclined angle”. So that means that spiral staircases are also misnamed.

3. Hold on! Screws have 300 times more holding power than nails. Screw threads cut into and deform the wood to hold tightly whereas nails grip with friction and their hold will loosen when the wood shrinks

4. Size matters: How are screws measured? Screws have three basic measurements: gauge, threads per inch (TPI), and shaft length in millimetres, although the first and last are most commonly used in the UK.

Gauge: this is determined by the thread diameter, not the diameter of the shaft

Length: for flat headed screws this is measured from the top of the head to the point of the screw. For screws with a raised head, this is measured from the underside of the head to the point.

TPI: the number of thread crests per inch
So, you may also see a measurement like 3.5 x 30mm. This means it’s a 3.5mm gauge, and 30mm long.

5. More than meets the eye: for such a small item, there’s a lot of engineering in a screw. Here are just some of the features we pack into our Performance Plus screws.


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