Expansion Anchor Drill Sizes
Expansion anchors (wedge anchors, drop-in anchors) require precise hole diameters for proper grip. The hole diameter must match the anchor's outer diameter exactly.
Wedge Anchor Size Chart
| Anchor Size | Drill Bit Ø | Min. Embedment | Hole Depth |
|---|---|---|---|
| M6 | 6mm | 30mm | 45mm |
| M8 | 8mm | 40mm | 55mm |
| M10 | 10mm | 50mm | 65mm |
| M12 | 12mm | 60mm | 80mm |
| M16 | 16mm | 80mm | 100mm |
| M20 | 20mm | 100mm | 125mm |
Drop-In Anchor Size Chart
| Thread | Drill Bit Ø | Anchor Length | Hole Depth |
|---|---|---|---|
| M6 | 8mm | 25mm | 30mm |
| M8 | 10mm | 30mm | 35mm |
| M10 | 12mm | 40mm | 45mm |
| M12 | 16mm | 50mm | 55mm |
| M16 | 20mm | 65mm | 70mm |
Chemical Anchor Drill Sizes
Chemical anchors (resin anchors) require oversized holes to allow resin to flow around the stud. The hole is typically 2-4mm larger than the rod diameter.
Chemical Anchor Size Chart
| Rod Size | Drill Bit Ø | Embedment | Hole Depth |
|---|---|---|---|
| M8 | 10mm | 80mm | 90mm |
| M10 | 12mm | 90mm | 100mm |
| M12 | 14mm | 110mm | 120mm |
| M16 | 18mm | 125mm | 140mm |
| M20 | 24mm | 170mm | 185mm |
| M24 | 28mm | 210mm | 225mm |
Important: Chemical anchors in hollow materials require special sleeves. Consult manufacturer specifications for screen tube diameters.
Sleeve Anchor Drill Sizes
Sleeve anchors (shield anchors) expand within the hole as the bolt is tightened. Hole diameter equals the sleeve's outer diameter.
Sleeve Anchor Size Chart
| Bolt Size | Drill Bit Ø | Min. Embedment | Hole Depth |
|---|---|---|---|
| M6 | 8mm | 35mm | 45mm |
| M8 | 10mm | 40mm | 50mm |
| M10 | 12mm | 50mm | 60mm |
| M12 | 14mm | 60mm | 75mm |
| M16 | 18mm | 75mm | 90mm |
Drilling Best Practices for Anchors
Hole Preparation
- Use hammer mode: Always use rotary hammer (SDS-Plus/Max) for concrete, not standard drills
- Mark depth: Use tape on bit to mark required depth
- Clean holes: Blow out dust with air pump—debris reduces holding strength by up to 50%
- Check diameter: Worn bits drill undersized holes; replace bits regularly
Material Considerations
- Solid concrete (C20-C40): Standard embedment depths apply
- High-strength concrete (C50+): May require reduced spacing
- Hollow block/brick: Use sleeve anchors or chemical anchors with mesh sleeves
- Cracked concrete: Use approved anchors rated for cracked concrete
Common Mistakes to Avoid
- Drilling holes too shallow—always add 10-15mm for dust
- Using worn drill bits that create undersized holes
- Not cleaning holes before chemical anchor installation
- Overtightening expansion anchors (causes concrete to crack)
