The McAlpine Coupling 1.1/4 Mxf X 3" S12A-3" is a plumbing fitting used to connect a 1.1/4 inch male pipe thread to a 3 inch solvent weld pipe. The "Mxf" in the description refers to the fact that one end of the coupling has a male pipe thread, while the other end is designed to fit inside a 3 inch solvent weld pipe. The coupling is made by McAlpine, a UK-based manufacturer of plumbing and drainage products. The "S12A" in the description refers to the specific model of the coupling. Overall, this coupling is useful for connecting pipes of different sizes together securely, ensuring a leak-free connection. ・ Available in 1¼", 1½", and 2" sizes ・ Available in 1", 2" and 3" lengths ・ Ideal for extending height of a trap ・ Manufactured in Polypropylene