The 504021-1 is an ST coupling receptacle designed for either PCB or through-panel mounting. Constructed from nickel-plated, die-cast zinc, it provides a durable housing for fiber optic connections. This receptacle includes a metal alignment sleeve specifically for multimode applications and comes with a positioning ring to ensure proper installation. It is designed to accept common multimode active devices in TO-18, TO-46, and TO-52 packages, making it a versatile component for various fiber optic systems.