The HW4-J04 is an X Joiner designed for HW4 track systems, available in both white and black. This joiner is notable for allowing feed-in from behind the bend, enhancing layout flexibility. It's important to consider the polarity when ordering, with options for either left or right orientation. For a comprehensive solution, it's advisable to order both types. This joiner is a crucial component for versatile and customized lighting arrangements in various settings, both residential and commercial.