The Simpson HDIA Hollow Drop-In Internally Threaded Anchor is a flush-mount expansion anchor engineered for attaching 3/8-in. threaded rod to overhead and vertical surfaces in both hollow and solid base materials. Trusted by mechanical, electrical, and plumbing contractors, this anchor is purpose-built for suspending conduit, cable trays, pipe supports, fire sprinklers, and lighting fixtures from CMU, hollow-core plank, brick, normal-weight concrete, and lightweight concrete - making it one of the most versatile drop-in anchors available for commercial and industrial overhead applications.

Key Features

• Expansion design for hollow and solid base materials - anchors securely into CMU, hollow-core plank, brick, normal-weight concrete, and lightweight concrete, eliminating the need to stock multiple anchor types for mixed-substrate jobsites
• Internally threaded design - accepts 3/8-in. threaded rod and allows for easy bolt removal after installation, saving time during adjustments, repositioning, or future maintenance
• Flush-mount installation - sits flush with the surface once set, creating a clean, low-profile connection point that keeps suspended systems properly aligned overhead
• Die-cast Zamac 3 alloy shell with carbon-steel cone - combines a corrosion-resistant shell material with a hardened cone to deliver consistent expansion performance and reliable holding strength across approved base materials
• Compatible with dedicated setting tools - installs with the HDIASTH37 setting tool for hollow materials or the HDIASTS31-37 for solid materials, ensuring proper seating and consistent installation quality on every anchor
• Approved for a wide range of overhead suspension applications - rated for suspending conduit, cable trays, pipe supports, fire sprinkler systems, and suspended lighting, covering the most common MEP and life-safety hanging scenarios

Why This Product

• True multi-substrate versatility - the expansion design works in both hollow base materials like CMU and hollow-core plank and solid materials like brick and concrete, so crews can use a single anchor specification across varied overhead conditions on the same project
• Re-enterable threaded connection - the internally threaded anchor allows the bolt or rod to be removed and reinserted without disturbing the anchor itself, a practical advantage during system commissioning, inspections, or phased installations
• Engineered for the most demanding overhead MEP applications - explicitly approved for fire sprinkler systems, conduit runs, cable trays, and suspended lighting, giving specifiers and installers confidence that the anchor meets the demands of code-sensitive overhead work
• Backed by Simpson Strong-Tie engineering - Simpson provides dedicated, properly sized setting tools for both hollow and solid substrates, supporting correct installation practice and reducing the risk of improperly set anchors in the field

Specifications

• Manufacturer: Simpson Strong-Tie
• MPN: HDIA37
• 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: Carbon steel
• Packaging: Packs of 50 and Cartons of 200

Approved Applications

• Suspending conduit and cable trays from overhead concrete structures
• Attaching pipe supports and hangers to concrete ceilings or walls
• Installing fire sprinkler systems requiring anchored threaded rod
• Mounting suspended lighting fixtures to concrete or masonry
• Anchoring into CMU (concrete masonry units) and hollow-core plank
• Use in solid base materials including brick, normal-weight concrete, and lightweight concrete

Frequently Asked Questions

What size hole do I need to drill for the Simpson HDIA37 anchor?

The HDIA37 requires a 5/8-inch diameter drill bit to create the proper hole for installation.

What rod or bolt size is compatible with the HDIA37?

The HDIA37 is designed to accept a 3/8-inch diameter threaded rod, with 16 threads per inch (TPI).

What setting tools are required to install the HDIA37?

For hollow base materials such as CMU and hollow-core plank, use the HDIASTH37 setting tool. For solid base materials such as brick and concrete, use the HDIASTS31-37 setting tool.

What base materials is the HDIA37 suitable for?

The HDIA37 expansion anchor is designed for use in both hollow and solid base materials, including CMU, hollow-core plank, brick, normal-weight concrete, and lightweight concrete.

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