The Simpson HDIA Hollow Drop-In Internally Threaded Anchor is a flush-mount expansion anchor from Simpson engineered for attaching threaded rod to overhead and wall-mounted systems including conduit, cable trays, pipe supports, fire sprinklers, and suspended lighting. What sets this anchor apart is its expansion design, which allows reliable anchoring in both hollow base materials - such as CMU and hollow-core plank - and solid base materials including brick, normal-weight concrete, and lightweight concrete, giving contractors a single, dependable fastener solution across a wide range of substrate conditions.

Key Features

• Compatible with hollow and solid base materials - anchors securely into CMU, hollow-core plank, brick, normal-weight concrete, and lightweight concrete, reducing the need to stock multiple anchor types for different substrates
• Internally threaded design - accepts a 5/16 in. threaded rod and allows for straightforward bolt removal and reinstallation without damaging the anchor, simplifying future adjustments or maintenance
• Flush-mount installation - sits flush with the surface after setting, creating a clean, low-profile connection point that works well in tight overhead clearance situations
• Die-cast Zamac 3 alloy shell with carbon-steel cone - combines a durable, corrosion-resistant shell with a hardened cone for consistent, reliable expansion and load transfer
• Dedicated setting tool compatibility - installs with the HDIASTH31 setting tool for hollow materials or the HDIASTS31-37 for solid materials, ensuring proper seating and full expansion in each base material type
• Approved for a broad range of suspension applications - suitable for suspending conduit, cable trays, pipe supports, fire sprinklers, and suspended lighting, making this anchor a practical choice across mechanical, electrical, and plumbing trades

Why This Product

• One anchor, multiple substrates - the expansion design works in both hollow materials like CMU and hollow-core plank and solid materials like brick and concrete, so crews can carry a single anchor type to handle varied field conditions without switching products mid-job
• Built for overhead suspension systems - specifically designed for attaching threaded rod to support conduit, cable trays, pipe supports, fire sprinklers, and suspended lighting, addressing the most common overhead fastening needs in commercial and industrial construction
• Internally threaded for lasting utility - the internal thread configuration lets workers remove and reattach the threaded rod without pulling or destroying the anchor, which protects the substrate and saves time on projects requiring periodic access to suspended systems
• Trusted Simpson engineering - manufactured by Simpson, a brand with a long track record in structural and fastening solutions, providing confidence that the anchor meets the performance expectations of professional installers across concrete and masonry applications

Specifications

• Manufacturer: Simpson Strong-Tie
• MPN: HDIA31
• Rod / Bolt Diameter: 5/16 in.
• Threads Per Inch (TPI): 18
• Length: 1-1/4 in.
• Drill Bit Diameter: 5/8 in.
• Shell Material: Die-cast Zamac 3 alloy
• Cone Material: Carbon steel
• Packaging: Packs of 50 and Cartons of 200

Approved Applications

• Suspending conduit and conduit supports from concrete ceilings or walls
• Attaching cable trays to hollow-core plank or CMU substrates
• Installing pipe supports and fire sprinkler systems in concrete overhead structures
• Mounting suspended lighting fixtures to normal-weight and lightweight concrete
• General threaded rod attachment in brick, CMU, hollow-core plank, normal-weight concrete, and lightweight concrete

Frequently Asked Questions

What base materials is the Simpson HDIA31 anchor compatible with?

The HDIA31 is designed for use in both hollow and solid base materials. It anchors effectively into CMU, hollow-core plank, brick, normal-weight concrete, and lightweight concrete, making it a highly versatile choice for a wide range of construction substrates.

What rod or bolt size does the HDIA31 accept?

The HDIA31 accepts a 5/16-inch diameter threaded rod with 18 threads per inch (TPI). A 5/8-inch drill bit is required to create the pilot hole for installation.

What setting tools are required to install the HDIA31?

Installation requires a dedicated setting tool. Use the HDIASTH31 setting tool for hollow materials such as CMU and hollow-core plank, or the HDIASTS31-37 setting tool for solid materials such as brick and concrete.

Can the bolt or rod be removed after the HDIA31 anchor is set?

Yes. Because the HDIA31 is internally threaded, the threaded rod or bolt can be removed and reinserted as needed without disturbing the installed anchor shell. This makes it easier to adjust or service suspended systems after installation.

Note: Product dimensions may differ from picture. Please see the item description above for specifications.