Stress wave loaded specimens are extensively used to study the dynamic fracture of a variety of materials. Various geometries can be found in the literature, each having its advantages and disadvantages. The majority of the available specimens are lacking the ability to propagate long cracks under pure mode I. Here, we present a newly developed specimen for dynamic mode I fracture tests. The new specimen has its advantages in being robust, easy to manufacture and having a well-defined crack path, which is repeatable as well as predictable. The proposed specimen has another advantage of propagating a crack under pure stress wave loading while utilizing a very simple experimental setup. The applicability of the specimen is presented through a series of dynamic fracture experiments on PMMA at crack velocities between 250 and 700 m/s.