Shown on the left side is the internal construction of a hollow piston pogo pin which involves drilling the piston to create additional space for the stainless-steel spring. By using a hollow piston design, the pogo pin can save space compared to traditional solid piston designs. The main advantage of a hollow one is also its biggest weakness: it can result in an unstable contact point between the piston and the barrel. In construction, the piston is always cantilevered on one side, creating a rigid and inflexible contact point. If there is any movement or misalignment between the mating surfaces, the piston can rock and change the position of the contact point, leading to instabilities in the electrical connection. Using a beryllium copper spring in a pogo pin is one solution to minimize discontinuities in the electrical connection. Beryllium copper is a highly conductive material that can carry electrical current with minimal resistance. The wire section of the beryllium copper spring is typically around 0.14mm, making it difficult to limit the maximum contact resistance below 150 mΩ during shock and vibration. Use of hollow spring pins with beryllium copper springs is only appropriate in limited applications.