#Mechanical anchor

Best screws for concrete – overview and application

6 min

When fixing in concrete, you typically use mechanical anchors which can be loaded immediately after application while being resistant to temperature changes during the installation. Find out more about one of the best-in-class solutions – concrete screws.

This release focuses on a single type of mechanical anchors, designed specifically for this substrate, namely concrete screws.

Are you looking for other content?

Here you can learn what a bonded anchor is.

Are you interested in other types of mechanical anchors?

Find out what other types of mechanical anchors are in use here.

Not sure whether to choose a bonded or mechanical anchor?

Here you can learn which anchor to choose depending on the substrate.

Mechanical anchoring in concrete – characteristics

Concrete is both one of the hardest and most commonly used construction materials. While it is true that you should opt for bonded anchors to ensure the highest loads in concrete, metal anchors (either screw-in or hammer-in) are very often used even in industrial construction work or can be found in such elements of infrastructure as bridges, roads, and stadiums.

Mechanical anchoring in concrete is very convenient because installation work does not depend on the setting time of the chemical compounds applied. It also enables temporary installation, followed by removal or replacement of fasteners. Mechanical anchoring is fast and easy to handle, it requires no additional accessories, and it is not so sensitive to weather conditions. 

When it comes to anchoring in concrete, it is also very useful to know in what kind of concrete you will be working. The distinctive types of concrete are:

  • reinforced concrete,
  • cracked concrete,
  • non-cracked concrete,
  • non-reinforced concrete.

Regardless of the class and type of concrete, you can freely use screw-in mechanical anchors to fix a variety of elements in it, including structural, decorative, or special-purpose fixtures. However, you should keep in mind that only some of the concrete screws available in the market are engineered well enough to perform adequately in reinforced concrete as well.

Did you know that...?

The RHL-X concrete screws from Rawlplug can deliver their top load bearing capacity in both cracked and non-cracked concrete of classes C20/25–C50/60 (which is ETA certified).

What is a concrete screw?

Concrete screws are highly specialised mechanical anchors used to securely fix structural elements in concrete substrates. The distinguishing feature of such a screw-in anchor is that – as the name itself implies – it is screwed into the base material, so it can also be freely unscrewed (unlike other anchors). This type of mechanical anchor is also called a concrete bolt.

Concrete screws are used to fasten various components to concrete surfaces. They can be used in construction and renovation work, in garden furniture installation, and in many other applications. 

Concrete screws will also perform well where edge distances are small and where fixings are densely spaced.

R-hlx concrete anchor
Example of use of the R-HLX concrete screw.

Screw-in anchor vs throughbolt for cracked and non-cracked concrete

Concrete screws offer numerous advantages, including much more convenient installation and better performance than solutions such as throughbolts for concrete. Consider the following comparisons: 

  • The R-HLX screw of 10 mm in diameter is characterised by a higher load bearing capacity than a larger (12 mm) throughbolt. 
  • Concrete screws cause less stress in concrete than throughbolts.
  • Concrete screw-in anchors do not require any special-purpose spanner applying an appropriate torque, which makes them easier to install than throughbolts, and which minimises application errors and potential future scrap.

Find out how a screw-in anchor is installed.

Best screws for concrete? Introducing the R-HLX

What makes the concrete screws from Rawlplug special? The RHL-X is an innovative line of screw-in anchors designed for anchoring in concrete of even the highest strength class. They come in two variations, distinguishable by the head design:

  1. R-HLX-HF – hexagonal head screw with a washer,
  2. R-HLX-CS – countersunk head screw.

The entire range of lengths of the R-HLX screw provides a match for different fixing applications. Both variants of the R-HLX concrete screw are available in 3 diameters:

  • 10 mm,
  • 12 mm,
  • 14 mm.

R-HLX – new thread for high load capacity

The RHL-X self-tapping screw stands out mainly because of the innovative design of its threaded section. A single thread running from the bottom to the very top of the screw, terminated with special serration, provides excellent material undercutting as soon as the installation starts and makes fixing easier by ensuring very high load transfer.

  • The screw’s improved load bearing capacity is attributable to the optimised shape of its tip – the teeth which ensure efficient anchoring from the very beginning of the thread.
  • Extending over the entire length of the screw, the single thread delivers high load capacity and causes the loading force to be distributed evenly.
self-tapping concrete screw
This is what the special thread of Rawlplug's innovative R-HLX concrete screw looks like.

Other distinguishing characteristics of Rawlplug’s screw-in anchor

Not only is the R-HLX a self-tapping screw, but it also offers some other highly unique advantages:

  • undercutting teeth at the beginning of the thread for quick and easy fixing;
  • no ordinary electro-galvanised finish – the RHL-X concrete screw is zinc-flake coated without acid etching, which prevents the fastener from hydrogenation; the corrosion resistance class of this concrete screw from Rawlplug is C1–C4;
  • superior durability and load bearing capacity achieved through induction hardening and manufacture from carbon steel;
  • seismic category of C1 and C2*, which makes the screws suitable for application in earthquake-prone areas;
  • certified fire resistance.

*In ETA as of April 2024.

Learn more about the RHL-X!

Find out all there is to know about the new line of RHL-X concrete screws from Rawlplug.

Applications of the R-HLX concrete screws from Rawlplug

The R-HLX screw-in anchor from Rawlplug is typically used for fixing structural elements in any type of concrete:

  • cracked concrete of class C20/25–C50/60,
  • non-cracked concrete of class C20/25–C50/60,
  • reinforced and non-reinforced concrete,
  • as well as in stone (subject to tests).

It is an excellent mechanical anchor designed for installing the following elements in concrete substrates:

  • railings and balustrades,
  • ventilated facades,
  • formwork,
  • temporary joints,
  • stadium seats,
  • bumpers,
  • fences and gates,
  • steel structures and racks,
  • supports,
  • system components.

The R-HLX screw-in anchor proves most useful for permanent fixing of wooden or metal elements, as well as decorative or structural elements to concrete surfaces. It is suitable for relatively heavy loads.

The R-HLX can also come in handy in straight-through installation, where system components need to be attached to a concrete wall. And since it is easy to remove, it performs equally well in renovation or system alteration jobs.

application of concrete screws
The concrete screw can be used, for example, to fix metal shelving.

Installing smaller and lighter fixtures?

Fixing with the R-HLX screw-in anchors for concrete applications

The installation of the R-HLX screws is very simple and does not require special accessories or specific amount of time, this being the case of bonded anchors, where one must consider the setting time to make application effective. The installation process is completed in four simple steps. First, however, remember the following rules:

  • the hole diameter should be identical as that of the screw; e.g. use a 10 mm drill bit when fixing with a screw of 10 mm in diameter,
  • when using an impact drill bit, remember to blow the drillings out of the hole with a pump at least four times,
  • combine the right impact socket with the impact wrench you will use to tighten the screw,
  • be careful not to rupture the screw head while tightening.

Follow these steps when using the concrete screws from Rawlplug:

Follow these steps when using the concrete screws from Rawlplug:

  1. 1

    Start by drilling a hole using an impact or dustless drill bit to the correct diameter relative to the screw diameter (they should be identical; for example, when fixing with an M10 screw, use a drill bit of 10 mm in diameter).

  2. 2

    When using a dustless drill bit, you can proceed to step 3. Having used an impact drill bit, remove dust by blowing it out at least four times with a hand pump.

  3. 3

    Screw the anchor into the hole using an impact wrench with an adequate socket and tighten it as much as needed to make sure that the fixture is pressed securely against the substrate.

  4. 4

    Stop screwing when the screw head or washer fits tightly to the fixture or the substrate. You must not damage the head of the concrete screw. 

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