What is a Screw Anchor or Screwbolt and How To Install Them

pile of screw bolts and screw anchors  


So - What Are Screw Anchors / Screw Bolts


Firstly lets run over the naming conventions - Screw anchors and screw bolts are the same thing. 

Depending on which part of the world you're from depends on which name they're primarily called. 

Australia for instance calls them Screw bolts whereas America calls them Screw Anchors. 

For the sake of this article we will refer to them as Screw bolts (being that we're Australian) but keep in mind, they're the same thing.


So what are they?

Screw Bolts are concrete screw-in-anchors designed to self tap a thread into concrete and masonry products in order to fasten down objects.

Much the same way a wood screw would work, except these are significantly bigger and are designed to work into masonry subtrates rather than wood.


close up shot of screw in anchor or screw bolt cutting thread in concrete


They generally feature a hex head bolt style head (although now countersunk head styles and undercut head styles are growing in popularity)

A large washer type flange on the underside of the head to help distribute the load evenly

A wide coarse thread, sometimes reinforced sometimes not.

The thread is designed to cut directly into your masonry substrate much in the same way a screw would work into timber, anchoring down your object and fastening it securely to the subtrate.


Why are screw bolts so popular?


The simplest answer is usually the right one. They're easy, fast and they work great.

Screw bolt anchors are super efficient to install.

You simply drill a hole the same diameter as the shank of the screw bolts (ie M6 x 50mm screw bolt you drill a 6mm hole). Then you drive them directly into the concrete using a standard socket.

That's literally it.

No wrenches, no spanners or marking out. Drill, Drive, Done.

Not only are screw bolts fast and easy to install, they are incredibly strong anchors aswell. We have screw bolt anchors in our range load rated up to 2.2 tonnes per anchor!

They can also be used as a through fixing, meaning literally no marking out. Line up your post or batten where you'd like it to be fixed, drill a hole directly through your post or batten and into the concrete then drive a screw bolt anchor straight through both. 

Now screw bolt anchors aren't the strongest fastener in the world, they're very strong but theyre not the strongest so they're not quite suitable for all applications but they absolutely will be perfect in most.

screw bolt anchor diagram



Installation Method



how to install a screw bolt or screw in anchor correctly


  • Figure out which size you need. Screw bolt anchors are sized by Diameter of Shank x Length. Pro Tip - The diameter does not include the thread and the thread can be anywhere from 1mm to 2mm wide. If you have pre-drilled holes in a post always go down by 1 diameter size. ie we have 8mm holes in my posts, I'd choose an M6 screwbolt anchor as this will be most likely 7.5mm on the thread and we dont want the screw anchor thread to catch the post on the way in and damage it.


  • Pre-drill a hole (through the object) into the concrete. With screw in anchors or screwbolts always drill the hole into the masonry the same diameter as the screw anchor. Ie M8 x 50mm Screw bolt anchors require an 8mm drill hole - M10 x 50mm Screw bolt anchors require a 10mm drill hol


  • Get rid of the dust or any excess rubble that may be in the hole. Always drill your hole 20-30% longer than the screw anchors so that any excess waste falls to the bottom and does not impact the anchor installation. The cleaner the hole the better the fix. Pro-Tip if you're installing into soft blockwork such as bricks or besa block, turn the hammer off your drill and drill as slowly as possible. If you use an aggressive hammer drill the pilot hole will most likely be oversized and the screw anchor has less to substrate to grip onto.


  • Load your screw anchor into your socket on the end of your driver (impact drivers or torque wrenches work the best. Drive the screw bolt anchor directly through your object directly into your hole in the masonry. Depending on your application you may have to install the screw anchors to a specified torque. This should always be discussed with either your engineer or the manufacturer and this information will be able to be found on the screw anchor technical data sheets.


  • Make sure the screw anchor is tight. 


Thats it. Done. 

Super easy and effective.


If you want to find some more information on screw bolt or screw in anchors you can find our full range right here with more specific information: Concrete Screws and Screw Bolts

If you've read this and have determined that Screw Bolt Anchors are not correct for your type of application you can find a full range of all our various fasteners here: Fasteners




Thanks for reading our latest blog entry 

Best Regards,

The Scrooz Fasteners Team 









Leave a comment

Comments have to be approved before showing up