Custom 9-inch anchor bolt selection

What Is a 9-Shaped Anchor Bolt?

A 9-shaped anchor bolt, also known as a 9-bolt, 9-shaped anchor rod, or pigtail anchor, is an embedded anchoring fastener with a circular loop hook at one end. Its name comes from the finished shape resembling the Arabic numeral "9"—a threaded straight shank with a closed circular loop bent at the tail end.

Unlike the right-angle hook of a 7-shaped (L-shaped) anchor bolt, the 9-shaped bolt's tail end is a complete circular loop. This geometric difference delivers key engineering advantages. According to product technical documentation, 9-shaped bolts are forged in one piece with no welded weak points, and their pull-out and lateral-shift resistance far exceeds that of standard L-bolts. The 9-shaped embedded bolt is one of the primary shape categories of anchor bolts, alongside L-type, U-type, and welded types.

9-shaped anchor bolts are typically produced per the GB/T 799 anchor bolt standard system, or per mechanical industry standards such as JB/ZQ 4363-2006. This product is a non-standard custom type that can be flexibly sized to customer drawings.

Standard Systems

9-shaped anchor bolts are produced under two main standard systems, corresponding to general embedment applications and mechanical industry applications respectively:

GB/T 799-2020, Foundation Bolts

This is the general national standard for anchor bolts, issued on November 19, 2020, implemented on June 1, 2021, fully superseding GB/T 799-1988. The standard applies to anchor bolts with thread sizes M8-M72, property grades 4.6 and 5.6, and product grade C. Key updates: The 2020 edition raised property grades from 3.6 to 4.6/5.6, extended the size range from M48 to M72, and added hot-dip galvanizing (GB/T 5267.3) requirements.

JB/ZQ 4363-2006, Foundation Bolts

This is a mechanical industry standard, issued by the China Heavy Machinery Industry Association, implemented on May 1, 2007, superseding JB/ZQ 4363-1997. This standard specifically covers the dimensional series for 9-shaped anchor bolts and is the most directly referenced standard for 9-shaped products on the market. Unlike the general provisions of GB/T 799, JB/ZQ 4363 addresses mechanical equipment installation scenarios with more specific parameters for 9-shaped loop dimensions and shank forms (thick shank/thin shank).

Selection recommendation: For general building embedment, reference GB/T 799-2020 first; for mechanical equipment installation or when thick/thin shank options are needed, reference JB/ZQ 4363-2006.

Key Technical Features

Anchoring Mechanism of the Circular Loop

9-shaped bolts use one-piece forged construction with no welded weak points. Academic research (ScienceDirect, 2024) conducted systematic testing and finite element analysis on the anchoring mechanism of L-type and J-type anchors, and the conclusions have direct reference value for understanding the anchoring behavior of 9-shaped loops:

Embedment depth dependence of failure modes: Research shows that anchor failure mode transitions with embedment depth. At shallow embedment (approximately 5d), concrete breakout failure dominates; as embedment depth increases, the failure mode gradually shifts to bolt shank tensile failure. The circular loop of a 9-shaped bolt provides a larger anchoring contact area at the same embedment depth, helping delay the onset of concrete breakout failure.

CCD design method: Research recommends the Concrete Capacity Design (CCD) method for calculating concrete breakout capacity, with a cone spread angle of 35°. This method applies to anchors with embedment depth less than 250 mm and is the basis of ACI 318 Appendix D.

Engineering significance of embedment depth and hook: Industry documentation explicitly states that both embedment depth and the hook serve to ensure friction between the bolt and foundation, preventing pull-out failure. For plain round anchor bolts, embedment depth is typically 25 times the diameter, with a hook length of approximately 120 mm. The circular loop of a 9-shaped bolt provides greater developed length and contact area at the same hook length.

Shank Forms: Thick Shank and Thin Shank

The JB/ZQ 4363-2006 system distinguishes between thick shank and thin shank forms:

The thick shank's unthreaded section mates with the hole wall for better shear performance and locating precision; the thin shank carries load over a smaller cross-section under tension, suited to pull-out-dominated anchoring.

Materials and Property Grades

Per GB/T 799-2020 and industry practice, material and grade options for 9-shaped anchor bolts are as follows:

The core position of Q235: Q235 steel is the primary material for anchor bolts due to its ease of machining, good ductility, and suitability for various working environments. Although rebar (Q345) offers higher strength, thread machining is more difficult—plain round bar (Q235) is easier to tap.

Heat treatment requirements for Grade 8.8 and above: Grades 8.8 and above require quench and temper heat treatment to achieve. 40Cr alloy steel, quenched and tempered, can reach Grade 8.8 or 10.9.

Dimensional Parameters

Per the JB/ZQ 4363 system and 9-shaped anchor bolt product data:

Marking example (per GB/T 1237 rules): For a foundation bolt with thread size d=M20, nominal length l=400 mm, property grade 4.6, plain finish: Foundation bolt GB/T 799 M20×400.

Manufacturing Process

Loop Forming

One-piece forged construction: Premium 9-shaped bolts use Q235 carbon steel forged in one piece, with no welded weak points, significantly improving structural strength—pull-out and lateral-shift resistance far exceed standard L-bolts. For large-diameter bolts (M24 and above), the bar is heated to forging temperature before loop bending to ensure no cracks or stress concentration in the loop area.

Welded loop: Some large-size or special-requirement products use welded loop connections. Weld quality must meet applicable standard requirements.

Threading

Thread tolerance grade is 4h or 5g, with product grade A or C. Rolled threads are typically used for higher strength and better fatigue resistance.

Surface Finishes

Per the technical conditions comparison between GB/T 799-2020 and the 1988 edition:

Application Areas

Equipment Foundation Anchoring

The most typical application for 9-shaped anchor bolts is securing small to medium-sized equipment to concrete foundations, suitable for equipment without strong vibration or impact. Fixed anchor bolts are cast together with the foundation. Typical equipment includes pumps, fans, and small machine tools.

Solar and New Energy

Hot-dip galvanized 9-shaped anchor bolts suit solar tracker support columns and other outdoor anchoring scenarios, with high anchoring strength and corrosion resistance for long-term service.

Steel Structure Column Bases

Used for steel structure factory column bases and steel structure foundation embedments. The loop provides reliable pull-out anchoring in the concrete foundation, ensuring column stability under wind and seismic loads.

Street Lighting and Traffic Infrastructure

Foundation embedment for street lights and traffic signs. These applications carry relatively light loads, and the compact 9-shaped structure fits the limited space at pole bases.

Bridge Crane Rails

The compact loop angle of 9-shaped anchor bolts makes them particularly suited to bridge crane rail fastening. Where rail bolts are densely arranged, the 9-shaped type saves more space than the L-type.

Bridge Engineering

304/316 stainless steel 9-shaped anchor bolts are used in bridge engineering fasteners, providing a corrosion-resistant anchoring solution.

Power Infrastructure

Suited to transmission and distribution tower foundations and other scenarios requiring high anchoring capacity.

Selection and Construction Guidelines

Key Selection Parameters

Construction Notes

1. Installation method: Fixed anchor bolts are cast together with the foundation; movable anchor bolts are used for heavy equipment with strong vibration and impact

2. Positioning and fixing: For high-precision requirements, first fabricate a positioning template, thread the bolts through, and adjust elevation to drawing requirements

3. Expansion anchor requirements: Foundation strength must be no less than 10 MPa, and the distance from bolt center to foundation edge must be no less than 7 times the diameter

4. Thread cleanliness: Product threads should be kept clean before use

5. Tightening requirements: Wrench force direction must align with the screw axis—never at an angle; force must not exceed safe torque and must be applied evenly

Ordering Information

1. Standard reference: GB/T 799-2020 or JB/ZQ 4363-2006

2. Specification: Thread diameter d × length L

3. Shank form (if referencing JB/ZQ 4363): Thick shank/thin shank

4. Material grade: Q235 / Q345 / 45# / 40Cr / 304 / 316

5. Property grade: 4.6 / 5.6 / 8.8 / 10.9

6. Surface finish: Plain / oxide / zinc plated / hot-dip galvanized

7. Drawing: Loop diameter, overall length, thread length

Summary

9-shaped anchor bolts are produced under two main systems: GB/T 799-2020 (general national standard) and JB/ZQ 4363-2006 (mechanical industry standard). GB/T 799-2020 applies to M8-M72, Grades 4.6/5.6, Grade C general anchor bolts, with hot-dip galvanizing added in the 2020 edition. JB/ZQ 4363-2006 specifically covers 9-shaped products in thick-shank and thin-shank forms with their dimensional series.

9-shaped bolts use one-piece forged construction, and the circular loop provides a larger anchoring contact area and better mechanical interlock in concrete than the L-type. Failure mode transitions with embedment depth: shallow embedment (approximately 5d) leads mainly to concrete breakout failure, while deep embedment shifts to bolt shank tensile failure; the CCD design method recommends a cone spread angle of 35°.

Q235 carbon steel is the primary material due to its ease of machining and good ductility—plain round bar is easier to tap than rebar. Grade 8.8 and above require quench and temper heat treatment. Embedment depth is typically 25 times the diameter, with a hook length of approximately 120 mm. For large diameters (d>45 mm) with excessive embedment depth, a square plate should be welded at the end.

This product is a non-standard custom type—loop diameter, length, and thread are all adjustable to drawing. It is widely used in equipment foundations, solar supports, steel structure column bases, street lighting and traffic infrastructure, bridge crane rails, bridge engineering, and power infrastructure.