Key takeaways
- Use the exact drill bit size specified for the screw; oversize holes lose most of the holding power.
- Drill 6–13 mm deeper than the embedment and blow the dust out.
- Keep at least 10 diameters from edges and from other anchors.
Concrete screws are simple to install, but four details decide whether a fixing holds 50 kg or 500 kg.
Drill bit size
| Screw | Carbide bit |
|---|---|
| 3/16" (4.8 mm) | 5/32" (4 mm) |
| 1/4" (6.3 mm) | 3/16" (5 mm) |
| 7.5 mm frame screw | 6 mm |
| 10 mm screw anchor | 8 mm |
Worn bits drill undersize holes and make screws snap; new bits wander and drill oversize in soft brick. Check the bit diameter.
Depth and cleaning
Drill at least 6 mm deeper than the screw will go, and blow or vacuum the dust out. Dust packed at the bottom stops the screw before full embedment.
Embedment and spacing
Use a minimum embedment of 25 mm for light fixings, 32–44 mm for heavier ones. Keep 10 screw diameters from an edge and between screws so the concrete cone does not crack.
Driving
Use a drill-driver or impact driver at moderate speed. Stop when the head is snug; over-torquing strips the thread you just cut.
Frequently asked questions
Can concrete screws be used in hollow block?
Yes, with care. Use a longer screw so threads engage both block walls, and drill without hammer action to avoid blowing out the inner wall.
Are concrete screws suitable for overhead fixings?
Only screws with a specific approval for overhead or safety-critical use. Ask us for approved screw anchors for those applications.
