M20 Drop in Anchor Bolts 304 Stainless Steel Heavy Duty Expansion Bolt for Construction with OEM Customization

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What Are Drop In Anchor Bolts?

Drop in anchor bolts are internally threaded expansion anchors designed for installation into solid base materials like concrete and stone . They consist of a cylindrical metal shield with a pre-assembled internal expander plug and slots at the bottom . During installation, drop in anchor bolts is placed into a pre-drilled hole flush with the surface. Driving a setting tool downward forces the plug to expand the slotted section against the hole wall, creating a secure mechanical hold . This design allows for a bolt or threaded rod to be inserted and removed as needed while the anchor body remains fixed in place . They are classified as displacement-controlled expansion anchors .

Materials

• Carbon Steel: The most common material. Available in various strength grades such as 4.8, 8.8, and 10.9 . Often used for general indoor industrial applications.

• Stainless Steel (Type 304/303): Provides good corrosion resistance for indoor and mild outdoor exposure where moisture is a concern .

• Stainless Steel (Type 316): Offers enhanced resistance to chlorides and harsh chemicals, making it suitable for marine environments and chemical plants .

• Zamac Alloy: A zinc-based alloy used in specific hollow drop in anchor bolts designs for base materials like concrete block .

Surface Finishes

• Zinc Plated (Clear/Yellow): A standard, cost-effective finish for carbon steel anchors, providing moderate corrosion resistance for dry indoor conditions . Yellow zinc plating offers an iridescent appearance and increased protection .

• Plain (Uncoated): The standard finish for stainless steel anchors, relying on the material’s natural oxide layer for corrosion resistance .

• Mechanical Galvanizing: A coating applied to high-strength steel to provide corrosion protection without the risk of hydrogen embrittlement.

• Specialty Coatings: Options like black phosphate, grey phosphate, black zinc, and Dacromet are available for specific performance or environmental requirements .

Specifications

• Diameter Range: Typically available from M6 to M24 in metric sizes  and from 1/4-inch to 3/4-inch in imperial sizes .

• Lengths: Vary by diameter and application, with common metric lengths from 25mm to 80mm  and imperial lengths from 3/4″ to 2″ for minimum embedment .

• Thread Types: Feature internal threads, most commonly national coarse (UNC) for inch-series bolts or metric coarse threads for metric bolts and rods .

• Head Style: Available with a “lipped” top for consistent flush installation or a “lipless” smooth top for mounting flush with or below the surface .

• Installation Tool: Requires a specific setting tool to properly expand the anchor against the base material .

Application Areas

• Overhead Suspensions: Securing overhead assemblies such as ductwork, pipe hangers, cable trays, conduits, and fire sprinkler systems, as the internal plug maintains position even when inverted .

• Anchoring Fixtures: Fastening handrails, door stops, and equipment to concrete floors and walls .

• Structural Connections: Used in new construction, restoration, and retrofits to attach structural elements to concrete, hollow-core slabs, and concrete masonry units (CMU) .

• Formwork Applications: Coil-thread versions are specifically designed to accept coil rods for use in concrete formwork systems .

• Shallow Embedment Needs: “Mini” drop-in anchors are ideal for applications requiring shallow embedment, such as in post-tensioned concrete slabs or precast hollow-core planks .

An Excellent Case: Prefabricated MEP Module Installation

Situation: A construction project in Singapore required the installation of prefabricated mechanical, electrical, and plumbing (MEP) modules along a challenging, steep stairway location. The goal was to improve on-site productivity and reduce installation time .

Task: The team needed a fastening solution that was reliable for overhead suspensions, could be installed efficiently in a difficult environment, and would provide a secure point for threaded rods of varying lengths to support the MEP services .

Action: Engineers designed prefabricated modules using Walraven drop in anchor bolts. These anchors were chosen for their internal threading, which allowed for easy adjustment and alignment of the suspended services during the coupling process. The anchors were installed flush into the concrete structure, providing a clean and secure mounting point for the threaded rods that supported the channel and pipe clamps .

Result: The use of drop in anchor bolts facilitated a highly efficient installation. A 20-meter stretch of MEP services, divided into 8 modules, was completely installed from first fix to handover in just three workdays. This method significantly boosted on-site productivity and minimized material wastage.