How to choose correct drill bit size for screw and wallplug?


Did I need a stronger Drill?

Perhaps not, often you can just lubricate the screws before driving them. People suggest soap, I've sometimes dipped screws in a light grease (which can leave marks on the wood). This really makes a huge difference.

Another alternative is to drill small pilot holes before inserting the screws. The width of the drill needs to be less than the full width of the screw threads.

If you are driving a lot of screws and wish to avoid these extra steps, I'd buy a stronger drill/driver.

What type of drill would be advisable

You might own a Bosch 7.2V screwdriver (model PSR7.2-LI) that has a torque (turning strength) of 6 or 10 Nm.

A 10.8V Bosch GSR 10,8 V-EC HX has a torque of 20 or 18 Nm.

A 14.4 V PSR 1440LI-2 has a torque of 17 or 34 Nm.

(The two ratings are usually for hard and soft materials)

You could buy a tool with a higher torque rating. Usually this is associated with a higher voltage...

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Using wallplugs and hole drilling advice from Fred In The Shed

Drilling Holes and Using Wallplugs

DIY help from Fred-in-the-Shed

How to chose a power drill

Also the latest and best cordless drills

Updated 26th January 2017

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Image below shows drill with one larger battery

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You can find cheaper 18v Combi drills but not with this specification

large 13mm chuck, 55NM of torque -no gimmicks just the grunt you need.

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Drill bits can be made in any size. Manufacturers routinely producing drill bits follow the defined sets of sizes defined by various...

The drill press is a machine that raises and lowers a spinning drill bit toward a table. This tool’s purpose is to...

A wood screw has a thread wrapped around a cylindrical shaft. For proper wood joinery, a hole must be drilled in the...

Taps are used to cut threads for bolts or screws into wood, plastic and metal. A hole of a specific size is...

To use a drill, you have to know how to choose the correct size bit, the right bit for the material you're...

Bolts are fasteners that are used in areas where strength counts the most. A properly installed bolt will not come loose until...

Drilling machines use drill bits to cut holes through materials such as wood and metal. These drill bits come in a...

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Many novice woodworkers make the mistake of drilling screws into boards without first creating a pilot hole, through which the screw can travel with less friction and less risk of cracking the board. The correct drill bit size needs to be chosen in order to create a correctly sized pilot hole, and choosing the right size is not exceptionally difficult. If the wrong size drill bit is chosen, the woodworker runs the risk of splitting the board, or creating a hole that is too large and therefore not able to give the screw enough wood to grip into.

The right drill bit size will depend on the size of the screw, if one is being used, as well as the intended purpose of the drilling. To choose the right drill bit size for a screw, you can either obtain a drilling chart that outlines which size drill bit is most appropriate for the size of screw being used, or you can make the measurement by eye. Start by laying out a few bits that are similar in size to the diameter of the screw...

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Drill presses are one of the most common industrial metalworking tools, but without the right drill bit, these tools are no more valuable in a factory than a paperweight. Even worse, the wrong drill bit can damage a workpiece instead of help finish it. With the wide variety of drill bits that are available on the market, it can be a bit tricky to select the best possible bit for the application. As a result, a bit that is "good enough" is all too often used, rather than the bit designed for the material and type of drilling.

While jobber-length, high-speed steel drill bits in fractional and millimeter sizes are the most common drill bits on the market, they are not necessarily the best. These are all-purpose drills which can be used for a wide variety of applications. However, for some applications, other types of drill bits can do a much better job.

The major factors in selecting the right type of drill bit to use for a job are the material type, hole size, hole...

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A slotted drive is characterised by a single straight recess across the screw’s head.

On the left is an example of a countersunk screw with a slotted drive.

A slotted drive viewed from above.

Which screwdriver bit?

Slotted screws are designed to be driven by a screwdriver bit with a flat blade tip.

Ensure you select the correct size for your screw.


A Phillips drive is characterised by a cross-shaped recess with rounded edges at the cross sections.

On the left is an example of a countersunk screw with a Phillips drive

A Phillips drive viewed from above.

Which screwdriver bit?

A screw with a Philips drive is designed to be driven with a Philips screwdriver bit.

Ensure you select the correct size bit for your screw.


A pozidriv drive looks very similar to a Phillips one, and also...

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Thx for the A2A...

I live in the land that sent a man to the moon, might nominate Trump and uses archaic terms...

I think a 4mm screw is kind of what I'd call a # 6, so I'd look at the rawl box and see what size goes with what screw, what size masonry bit is suggested and just wing it from there.

In critical applications I ascertain.

The diameter and count of the mounting holes available on the item to be installed. Ascertain the weight of the item being installed. Verify what I am anchoring into. See if the manufacturer of this item has mounting directions. If no on #4, google up the maker of the the plugs, inserts, shields, Rawls, Hiltis, Redheads... I'm considering using and match methods and materials to my application...

Back in the dawn of time we used wooden dowels or lead wool punched into holes drilled in concrete... Years later we held onto catalogs, Now it's a science and the info is very accessible on whatever device you are using to read...

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The plugs are for fixing screws into masonry, so the drill you are using is a masonry drill. These are usually sized in Metric diameters, and the diameters correspond to the plug sizes.

Screws are sized in 'Guage' (width of the threaded part) X Length (which can be in mm or inch). The guage sizes approximately correspond to appropriate hole & plug (metric)diameters. However, different combinations of 'masonry', thread profile, and plugging materials can affect the 'fit' of a particular screw.

Unfortunately, there are no standard colour codes for the sizes, but I think that Rawlplug use (in the UK) brown for an 8 and red for a 6.

Some other manufacturers make all their plugs in the same colour, but helpfully mould a number into the plug, which indicates the correct drill diameter. Some plugs are also supplied moulded onto a 'card' or a 'spine', which will often include funny-shaped holes or cutouts that are meant to act as a guide to selecting the right plug & hole...

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