Made of 7/8 inch diameter stainless steel. The 18x6 denotes that the piece is 18 inches long with a 6 inch offset. The component that is connected to the of the S-Bend Tube will sit up 18 inches up and 6 inches over from the placement of the mounting clamp (if clamped at the end of the tube). Using a 7/8 inch stainless steel tube for the initial part of a switch mount gives a greater stiffness over using the smaller diameter stems for the entire distance.