The Simpson HDIA37SS Hollow Drop-In Internally Threaded Anchor is a flush-mount expansion anchor engineered for attaching 3/8-inch threaded rod to overhead structures in both hollow and solid base materials. Designed by Simpson Strong-Tie, this anchor is built for mechanical and electrical suspension applications including conduit, cable trays, pipe supports, fire sprinklers, and suspended lighting. Its expansion design performs reliably across a broad range of substrates - from CMU and hollow-core plank to brick, normal-weight concrete, and lightweight concrete - making it a dependable single-anchor solution for mixed-substrate job sites. The die-cast Zamac 3 alloy shell pairs with a Type 304 stainless-steel cone to deliver corrosion resistance where it matters most.

Key Features

• Expansion design anchors into hollow and solid base materials - works in CMU, hollow-core plank, brick, normal-weight concrete, and lightweight concrete, eliminating the need to stock multiple anchor types for different substrates
• Internally threaded design accepts 3/8-16 threaded rod - allows the rod to be fully removed and reinserted without disturbing the anchor, simplifying adjustments and future maintenance
• Flush-mount installation profile - sits level with the base material surface for a clean, low-profile connection that does not interfere with adjacent structure or finishes
• Die-cast Zamac 3 alloy shell with Type 304 stainless-steel cone - the stainless cone provides corrosion resistance suited to mechanical rooms, utility spaces, and other demanding environments
• Compatible with dedicated setting tools for hollow and solid materials - installs correctly with the HDIASTH37 setting tool for hollow materials or the HDIASTS31-37 for solid materials, ensuring consistent, reliable expansion every time
• Sized for common suspension applications - the 5/8-inch drill bit diameter and 1 1/4-inch anchor length are matched to standard 3/8-16 threaded rod used across conduit, cable tray, and pipe hanger systems

Why This Product

• One anchor, multiple substrates - the expansion design is engineered to anchor into hollow materials like CMU and hollow-core plank as well as solid materials like brick and concrete, reducing the complexity of specifying and purchasing different fasteners for each base material on a project
• Built for frequent-access suspension points - the internally threaded design allows bolt removal without disturbing the installed anchor, which is a practical advantage in conduit, cable tray, and sprinkler installations where future access or reconfiguration is expected
• Corrosion-resistant construction for demanding environments - the Type 304 stainless-steel cone is well suited to the moisture-exposed and chemically active conditions common in mechanical rooms, utility ceilings, and overhead concrete structures
• Engineered by Simpson Strong-Tie for suspension applications - specifically designed for suspending conduit, cable trays, pipe supports, fire sprinklers, and lighting, giving engineers and installers confidence that the anchor is matched to these exact application demands

Specifications

• Model Number: HDIA37SS
• Bolt/Rod Diameter: 3/8 in.
• Length: 1-1/4 in.
• Drill Bit Diameter: 5/8 in.
• Threads Per Inch (TPI): 16
• Shell Material: Die-cast Zamac 3 alloy
• Cone Material: Type 304 stainless steel
• Packaging: Packs of 50 and Cartons of 200

Approved Applications

• Suspending conduit and conduit racks from concrete ceilings and overhead structures
• Attaching cable trays and wire management systems to concrete or CMU
• Supporting pipe hangers and pipe supports in mechanical rooms and utility spaces
• Installing fire sprinkler drop-rod connections into concrete overhead
• Mounting suspended lighting fixtures to concrete, brick, hollow-core plank, and CMU
• Any application requiring a flush-mount, internally threaded anchor accepting a 3/8-inch threaded rod

Frequently Asked Questions

What base materials is the HDIA37SS compatible with?

The HDIA37SS expansion design allows it to anchor into a wide range of base materials, including CMU (concrete masonry units), hollow-core plank, brick, normal-weight concrete, and lightweight concrete - making it suitable for both hollow and solid substrates.

What size threaded rod does the HDIA37SS accept?

The HDIA37SS is designed to accept a 3/8-inch diameter threaded rod with 16 threads per inch (3/8-16 TPI threading), which is a common standard size used in conduit, cable tray, and pipe support suspension applications.

What drill bit size is required to install the HDIA37SS?

A 5/8-inch diameter drill bit is required to bore the correct hole for installing the HDIA37SS anchor. Using the correct bit size ensures proper expansion and load performance of the anchor.

What setting tool is needed to install the HDIA37SS?

For installation in hollow materials, use the HDIASTH37 setting tool. For installation in solid materials, use the HDIASTS31-37 setting tool. Using the appropriate setting tool ensures the anchor expands correctly and seats flush with the surface.

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