A stainless steel muff coupling, also known as a sleeve or box coupling, is a type of rigid mechanical coupling used to connect two shafts for power transmission. It consists of a hollow cylinder (the sleeve) that is fitted over the ends of the shafts and secured with keys. The key transmits torque from one shaft to the other. Stainless steel is often used for its strength, corrosion resistance, and durability, making it suitable for demanding applications.