The paper extends the development of the split cantilever beam test specimen. The specimen is intended to measure the Mode III out-of-plane tearing interlaminar fracture toughness of composite materials. To help identify the effects of Mode I and Mode II in the specimen, the specimen end rotation, end opening, and adherend thickness are quantified experimentally. In addition, the crack-tip profile is determined using X-ray techniques, and the fracture morphology is identified as a function of location on the fracture surface.