Which Screws do I Use?

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There are a vast selection of screws available for the DIYer to choose from. Below is a brief description of what to look for, and what to take into consideration when buying screws for DIY projects around the home and elsewhere.

Let’s start by taking a look at the parts the make up a typical screw.

1) The screw head

There are two common types of screw head. The most popular one used these is days is the Phillips head (or cross head as it is sometimes referred to – on the right in the picture below). The second most popular type of screw is the slotted head or straight/flat head.

Fig 1

There are others available such as security head screws which can only be turned using a Torx or star bit, and there are anti vandal or one way screws which are very difficult to remove and are virtually a permanent fixing.

2) The screw head shape

There are countersunk head screws which have a flat head which is tapered underneath to give a flush finish. Once the screw is in place, the head of the screw will sit level with the surface.

Roundhead screws have, as you would expect, a roundhead with a flat underside so when used as a fixing the head stays above the surface.

Another head shape is the oval which has a less prominent rounded head and is tapered underneath, these could be used as an example for fixing brass door handles in place.

3) The gauge

Gauge refers to the width of the screw thread, typical sizes are 6s, 8s, 10s, 12s gauge so the higher the gauge the thicker the screw thread. When you buy premade items, some manufacturers include the screw gauge to use in their instructions – use 2″ 8 screws for example.

The gauge is always printed on the side of the packaging of pre-packed screws when you buy them from DIY and other stores.

4) The length

The length of the screw is measured from the tip of the screw to the underside of the head, typical lengths available are from 1/2 inch (12mm) to 4 inches (100mm) long.

Wood screws are usually made from hardened steel or brass and can be purchased with an anti-corrosion finish if required.

Below is a photo of various woodscrews available at most DIY stores and below that other types of screw, which you’ll also find at DIY stores.

WOODSCREWS
SCREWS

Choosing the right screw for the job

If you are fixing something to a wall the first thing you must do is to ascertain how heavy it is and what is the wall made of eg brick, plasterboard, thermal block etc.

Experience does go a long way to help you decide what size/type of screw and plastic rawlplug you should need and the more DIY you do the better your judgement will be.

The following examples of screw sizes should only be used as a general guide

Fixing brackets for kitchen cupboards to a plastered brick / block wall – use  2 1/2 ” x 10s countersunk cross head screws with Brown plastic rawlplugs and penny / mudguard washers (these steel washers are 1″ in diameter with a 1/4″ hole).

If the wall is dot and dabbed, as a lot of new build properties are, (plasterboard stuck to the wall) then you may need screws 1″ longer to allow for the void created by the plasterboard.

Fixing hinges to a softwood frame for an internal door use 1 1/4″ x 8s countersunk cross head screws in steel or brass depending on the hinge material. If you are fixing to a hardwood frame drill a 1/16″ pilot hole to the depth of the screw first.

Fixing a 3 foot long shelf to a brick wall, if the load on the shelf will be light, eg ornaments, use 1 1/2″ x 8s countersunk / roundhead (depends on the bracket) screws with red plastic rawlplugs. If the shelf is in a garage use 1 1/2″ x 10s screws with red rawlplugs as the load will no doubt end up heavy.

Hanging a 12″ x 8″ picture frame on a brick wall use a 1″ x 6s roundhead screw with a yellow plastic rawlplug.

Whenever you use a screw fixing you should always ‘feel’ the screw tighten up as you screw it in, if it feels loose, remove it and increase the screw gauge say from 6 to 8 using the same rawlplug, if this fails to improve the fixing you will have to increase both screw size and rawlplug.

Choose the appropriate length of screw for the job, if you are fixing a piece of timber to a wall there should be at least 2/3 of the screw in the wall.

Does the screw need to have an anti-corrosive coating for exterior work.

Will the screw be used as a fixing into hardwood, if so drill a pilot hole so the wood doesn’t split and the screw head doesn’t shear off (more common with brass screws).

A popular screw with both DIYers and professionals is the Phillips or cross head screw. They are ideal for use with battery drill / drivers and if the screw is being driven in by hand there is less chance of the screwdriver slipping and damaging the surface of whatever you are fixing in place.

Don’t be a cheapskate and buy the cheapest fixings available, good fixings cost a little more but will save you a lot of time and frustration. Most of the big DIY stores such as B & Q, Wickes, Focus etc, have vast ranges of good quality fixings.