Dyconn Faucet MH Series Washing Machine Outlet Box with stainless steel hammer arrest is designed to prevent water shockwaves caused by the washing machine's shut-off valve. The MH Series is constructed with lead-free brass for the valve body & amp; 304 stainless steel for the hammer arrestor's tube. By using 304 stainless steel for the hammer arrestor's tube, it ensures the inner wall of the tube will never rust or corrode like copper tubes. This reduces the possibility of adding unwanted friction to the arrestor ball inside the tube. All MH boxes come with an adjustable mounting bracket & amp; a snap-on faceplate to accommodate up to 3/4" of thick drywall. Two knock-out drain holes are designed in the center of the box (top and bottom)