Simpson HDIA37 Hollow Drop-In Internally Threaded expansion Anchor 3/8"The HDIA hollow drop in anchor is an internally threaded, flush mount expansion anchor designed for attaching threaded rod to support a variety of conduit, cables and lighting. This anchor is ideal for use with hollow base materials such as CMU and hollow core plank as well as in solid base materials such as brick and both normal weight and lightweight concrete. The HDIA can easily be installed in both hollow and solid materials with a setting tool.