Anchor Bolt Sizes (M6–M20) Explained

27 Sep , 2025

Anchor Bolt Sizes Explained: M6, M8, M10, M12, M16, M20 & More

Anchor bolts are fasteners that secure fixtures to concrete, brick, or stone. Common metric sizes—M6, M8, M10, M12, M16, and M20—cover light to heavy-duty jobs: the larger the diameter, the higher the holding capacity and embedment needed. Select the size based on load, base material, anchor type, embedment depth, and safety factor.

Ferry International has supplied high-quality anchor bolts for 60+ years from our Ghaziabad (U.P.) headquarters, serving customers across India and worldwide. We manufacture shield anchors (3-leaf, 4-leaf), brass anchors, drop-in anchors, through bolts, eye-hook anchors, and J-hook anchors for construction, oil & gas, power plants, and marine applications.

What Are Anchor Bolts?

Anchor bolts are mechanical or chemical fasteners that lock into concrete, brick, or stone to hold structural and non-structural elements—rails, machines, cable trays, facades, piping, and more. In metric sizing:

“M” denotes the outer diameter of the bolt in millimeters (e.g., M12 = 12 mm dia).
Performance depends on anchor type, embedment depth, concrete strength, edge distances, and installation quality.

Which Size Fits Which Job?

Use this as a starting point. Final selection should follow your load calculations, site conditions, and relevant codes.

Typical Need / Fixture	Suggested Size Range	Common Anchor Types	Notes
Light fixtures, cable clips, signage on masonry	M6 – M8	3-leaf/4-leaf shield, brass anchor	Short embedment; avoid close edges.
Handrails, brackets, small base plates	M8 – M10	Through bolt, drop-in, shield	Good for medium loads and repetitive installs.
Facade brackets, racking, light machinery	M10 – M12	Through bolt, drop-in, chemical	Check spacing and edge distance.
Pipe supports, ladders, guard rails	M12 – M16	Through bolt, chemical, heavy shield	M16 is a common “heavy duty” site choice.
Heavy machinery, structural steel seats	M16 – M20	Chemical, through bolt, cast-in J-bolt	Verify base thickness; consider dynamic loads.
Lifting eyes / temporary rigging points*	M16 – M20	Eye-hook anchor (rated), chemical	*Use only rated hardware and follow lift plans.

Always confirm design loads, safety factors, and local standards before finalizing.

Anchor Types We Manufacture (and When to Use Them)

1. Shield Anchors (Three-Leaf & Four-Leaf)

Best for: Medium loads in solid masonry/concrete.
How they work: Expanding sleeves grip the hole walls as you tighten.
Pros: Fast install, removable bolt; good for repetitive fixation.
Watch-outs: Avoid weak/porous substrates; respect edge distances.

2. Brass Anchors

Best for: Light to medium loads; interior applications.
Pros: Corrosion-resistant; clean threads; compact.
Watch-outs: Use with appropriate screws/bolts and controlled torque.

3. Drop-In Anchors

Best for: Flush-finish needs (e.g., threaded inserts in slabs/soffits).
How they work: A setting tool expands the internal plug.
Pros: Flush with surface; great for hangers and MEP supports.
Watch-outs: Requires correct setting depth and tool.

4. Through Bolts (Wedge/Expansion Anchors)

Best for: Reliable, heavy-duty fixings in cracked/uncracked concrete.
Pros: High shear/tension capacity; immediate loading.
Watch-outs: Hole diameter and embedment depth are critical.

5. Eye-Hook Anchors

Best for: Cable runs, light rigging, safety lines (as rated).
Pros: Integrated eye; tidy routing.
Watch-outs: Use only where load ratings and direction are appropriate.

6. J-Hook (Cast-in) Anchor Bolts

Best for: Foundations, base plates, columns, machinery seats.
Pros: Very high capacity; ideal for new pours.
Watch-outs: Requires accurate placement & templates before casting.

For complete details, click here to Download the Anchor Bolt Size Chart PDF.

Size, Embedment & Base Material: The Big 3

Size (M-diameter): Larger diameters (M16/M20) handle higher loads but require deeper embedment and more edge clearance.
Embedment Depth: Typical “rule of thumb” is 8–12 × diameter for mechanical anchors (project-specific). More embedment = more capacity—until concrete breakout governs.
Base Material:
Cracked concrete: Choose anchors tested/qualified for cracked substrates.
Uncracked concrete/solid brick: More options, but still check edge distances.
Hollow block/porous stone: Consider chemical anchors or specialized sleeves.

Pro Tip: If edge distance or spacing is tight, consider chemical anchors or drop-ins to reduce expansion stresses.

Step-by-Step: How to Choose the Right Anchor

Define the load: Dead + live + wind/seismic; include safety factor.
Know the substrate: Concrete grade, cracked/uncracked, thickness, condition.
Check geometry: Edge distance, spacing, embedment available, fixture hole size.
Select anchor type: Shield / through bolt / drop-in / chemical / J-bolt / eye.
Pick diameter: Start from the selector table; validate against load charts.
Set embedment: Follow manufacturer’s recommended ranges for your size/type.
Choose corrosion protection: Zinc-plated, hot-dip galvanized, stainless (A2/A4) for marine/chemical exposure.
Plan installation: Correct drill bit, hole cleaning, torque, and testing method.
Document: Record batch, torque values, and test results for QA/QC.

Installation (How-To) – Mechanical Anchors (Through Bolt / Shield / Drop-In)

Mark & drill the hole to the specified diameter and depth (check data sheet).
Clean: blow, brush, blow—repeat. Dust kills capacity.
Insert anchor: ensure correct orientation and depth; set drop-ins with the setting tool.
Position the fixture and tighten to specified torque using a calibrated wrench.

Verify: perform proof-loading or torque-check per your QA plan.the

For chemical anchors, add hole drying, adhesive injection (bottom-up), stud insertion with twist, and curing time before loading.

Common Mistakes to Avoid

Under-drilled or dusty holes → reduced expansion and slip.
Wrong edge distance/spacing → concrete breakout or splitting.
Over-torqueing → anchor spin, cone cracking, or sleeve damage.
Mixing metals (e.g., stainless bolt in plain steel sleeve) → galvanic corrosion.
Ignoring cracked concrete → use anchors qualified for cracked conditions.
No QA records → missing torque/test logs can fail audits.

Comparison: Anchor Types vs Typical Use

Anchor Type	Typical Sizes	Load Level	Best Use	Surface Finish
3-Leaf Shield	M6–M12	Light–Medium	Masonry fixtures, brackets	Bolt removable
4-Leaf Shield	M8–M16	Medium	Denser masonry, concrete	Bolt removable
Brass Anchor	M6–M10	Light–Medium	Interior, small fixings	Flush/clean
Drop-In	M8–M20	Medium–High	Hangers, soffits, threaded inserts	Flush with a slab
Through Bolt	M8–M20	Medium–High	Rails, machinery, structural seats	Proud of the surface
Eye-Hook	M8–M20	Light–High*	Routing/rigging (rated)	Eye visible
J-Hook Cast-In	M12–M30+	High	Foundations, columns	Cast-in

*Capacity depends on rating and direction of load—check data.

“To explore the complete range of anchor types, click here.”

Real-World Example (Simplified)

Task: Fix a pipe support bracket to a concrete wall in a power plant.
Loads: 2.0 kN tension, 3.0 kN shear, occasional vibration.
Constraints: 80 mm minimum edge distance; 120 mm wall thickness.
Choice: M12 through bolt (cracked-concrete rated), 100 mm embedment, stainless A4 due to humidity.
QA: Torque to spec; record torque value and anchor batch; re-check after 24 hours.

Pricing & Procurement Notes

Unit cost rises with diameter, length, and corrosion protection (HDG or stainless).
Project cost is often lower with standardized sizes (e.g., M10/M12/M16) and bulk ordering.
For marine/chemical environments, stainless (A4) minimizes lifecycle cost despite higher upfront price.
Ferry International provides custom lengths, coatings, and packing for site logistics.

Technical Specs You’ll Commonly Specify

Diameter (M6–M20) and usable thread length
Overall anchor length and min. embedment
Material & coating (Carbon steel zinc-plated / HDG / A2 / A4)
Hole diameter/tolerance
Required installation torque
Qualification (cracked concrete, fire rating, seismic category—if applicable)

FAQs

1) What size anchor bolt should I use for a handrail?
Most handrails on concrete use M10 or M12 through bolts or shield anchors, depending on loads and local code. Always check edge distance and base thickness before drilling.

2) Can I use M8 anchors for heavy machinery?
Usually no. Heavy machines typically need M16–M20 or cast-in J-bolts, sometimes paired with chemical anchoring for vibration resistance.

3) How deep should I drill for an M12 anchor?
Follow the anchor’s data sheet. As a rough guide, mechanical anchors may need ~8–12 × diameter embedment. For M12, that’s often 96–144 mm embedment, plus dust clearance.

4) Are drop-in anchors removable?
The insert stays flush in the concrete, but the threaded rod/bolt is removable. They’re popular where you want a clean surface and changeable attachments.

5) Which anchors are best near the sea or chemicals?
Use stainless steel A4 or hot-dip galvanized hardware. For severe exposure or splash zones, A4 stainless is commonly preferred.

6) Do I need different anchors for cracked concrete?
Yes. Choose anchors qualified for cracked concrete, especially in slabs or areas with tension zones and seismic action.

7) When should I choose chemical anchors instead of mechanical ones?
When you need high capacity, reduced edge stress, or you’re working with irregular holes/large diameters. Observe curing time before loading.

Conclusion

Choosing the right anchor bolt size is about matching load, base material, and anchor type—then installing with clean holes, correct embedment, and specified torque. For most projects, M10–M16 covers the bulk of needs, while M6–M8 suits lighter fixtures, and M20 handles the heaviest jobs.

Summary:

Pick size by load and geometry; confirm with data sheets.
Mechanical anchors (through bolts, shields, drop-ins) are fast and reliable.
Use stainless/HDG for harsh environments; record torque and tests for QA.

Need a size recommendation or bulk quote? Contact Ferry International for M6–M20 anchors and custom solutions (shield, brass, drop-in, through bolts, eye-hooks, J-hooks). Share your load, substrate, and drawing, and our team will size and supply—fast.

Have Query ? Reach Out Us!

Frequently Asked Questions

What are anchor bolts used for?

Anchor bolts are essential fasteners for securing structures like machinery, pipes, and more in place, ensuring safety and stability in construction and industrial projects.

What types of anchor bolts do you supply and where are they used?

We supply a wide range of anchor bolts like shield anchors, through bolts, brass anchors, drop-in anchors, eye hooks, and J-hooks. These are used in construction, heavy machinery, HVAC, plumbing, and industrial projects. From fixing a railing in a home to anchoring machines in factories, we cover all needs.

How do I select the right anchor bolt for my project?

The right anchor depends on your load, base material, and environment.1- For heavy-duty loads, use shield anchors or through bolts.2- corrosive areas, use stainless steel or brass anchors.3- For suspended fittings, go with drop-in anchors. If you share your project details, our team will be able to recommend the best fit.

Do you manufacture pipe clamps and hinges also?

Yes, along with anchor bolts, we also make pipe clamps and industrial hinges. Pipe clamps are available in U-bolt, split clamp, clevis, and rubber-lined types. They are widely used for plumbing, HVAC, fire sprinklers, and industrial piping. Hinges are made for industrial doors and heavy structures.

Can I order small quantities or only bulk?

We cater to both retail and bulk orders. Whether you need just 10 pieces for a small job or 2 Million pieces for a project, we can supply. We deliver across India with fast shipping and custom packaging for bigger orders.

What industries can benefit from your products?

Our products serve industries like construction, plumbing, HVAC, oil & gas, providing reliable and durable fasteners for various commercial and industrial projects.