Merchant Couplings – BMI & 316 Stainless Steel (Sch 40) Merchant couplings available in Black Malleable Iron (BMI) and 316 Stainless Steel Schedule 40 for secure, threaded pipe connections. Designed to join two male pipe ends, these couplings provide durable, leak-resistant performance in air, water, oil, gas, and general industrial piping systems. Suitable for maintenance, repairs, and new installations.