The ECS-40-20-1 crystal series from ECS Inc. International offers 4 MHz quartz crystals designed for both surface mount and through-hole mounting. These crystals are commonly found in a variety of electronic devices, particularly in circuits that require precise timing, such as microcontrollers, communication modules, and industrial control systems. If you're working on any project that needs a reliable 4 MHz clock signal, these crystals are a solid choice.

One thing worth noting is their versatility in packaging options. The availability in both surface mount and through-hole formats makes them adaptable to a wide range of PCB designs and manufacturing processes. Engineers tend to reach for these crystals when they need a compact solution for modern SMT assemblies but also want the flexibility to use them in older, more traditional through-hole boards. Another practical observation is their stability; 4 MHz crystals are known for their relatively low frequency, which means they maintain good accuracy over a wide temperature range, making them suitable for applications where environmental conditions might vary significantly.