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UNRAVELLING THE MYSTERY OF SCREWS!

How often have you started to do a small job in the house only to find you don't have a suitable screw!  They are either too fat, too long, not fat enough or not long enough.  If by some miracle the screw fits, you don't have a rawl plug!

A trip to the DIY shop beckons, but by the time you have found the screws, sorted out which size and which head shape you want, queued at the checkout and got home, there is no time left to do the job.

Sounds familiar - well here is a little bit of basic information which may help in future.

I must thank Mr. George Gouraud for the following information regarding a screw which I have omitted.

"It is a Canadian invention called the Robertson Head.  This screw has a square, flat bottomed "slot" and is available in all the sizes found in other head styles, as well as having 4" slot sizes.  The advantages of this type of head are:-

1:  It will not "cam out" as you tighten or loosen it, as happens with the Phillips head.

2:  The screw can be placed on the driver bit and will stay there even if you are driving it into either an overhead or downward facing work piece."

Thank you Mr. Gouraud.

 TIPS

• Here's a formula sent in by Geoff Sharpe, for working out the exact diameter, in inches, of the shank of a screw.

Multiply the screw Number by 0.013 and add 0.060.

Examples -

(No.) 8 x 0.013 + 0.060 = 0.164

(No.)10 x 0.013 + 0.060 = 0.190

My thanks to Jason Lee Olson for correcting the original formula shown

Jason has also suggested you could convert the screw number to to decimal
e.g. No. 8 = .008 and use the following formula.

Screw No. 8 - .008 x 13 + .060 = .164 (No. 8 diameter in inches)

Screw No. 6 - .006 x 13 + .060 = .138 (No. 6 diameter in inches)

Should you require the diameter in mm then multiply the answer by 25.4.

Screw No. 8 - .008 x 13 + .060 = .164 (No. 8 diameter in inches) x 25.4 = 4.166 diameter in mm

Screw No. 6 - .006 x 13 + .060 = .138 (No. 6 diameter in inches) x 25.4 = 3.505 diameter in mm

• Be sure to get the right screw for the job, particularly with regard to length.  Just a fraction too long can result in damage to a decorative surface or the screw coming right through to the other side. Too short and they may not be up to the job in hand.

• To make screws easier to remove at a later date, rub soap on the thread before screwing in.

Thanks to Geoff Smith of this one

We have, however, been advised that soap can attract moisture which results in the screw rusting, (see next tip).

• If you apply a little grease or Vaseline to the thread when inserting new screws they will be easier to remove should the need arise.   Do not use soap as this attracts moisture which can result in the screw rusting.

• To avoid splitting the wood make start holes before attempting to insert the screw.  This can be done with a bradawl for small screws in soft wood or, alternatively, with a very small drill bit.

• Avoid several screws following a wood grain as this can lead to the wood splitting down the grain.