The head tube contains the headset, the bearings for the fork via its steerer tube. A stem must be compatible with the dimensions of the fork steerer tube. The tube through which the steerer of the fork passes is called the head tube. An unthreaded steel steerer tube may be threaded with an appropriate die if necessary. Manufacturers of high-end bikes, both road and mountain, have started to use tapered steerer tubes. The original version, MC1, used a quill stem and required a threaded steerer. Others, notably Cannondale use a single shock built into the steerer tube above the crown. The steerer tubes are then cut to length to fit upon installation. This comprised a solid steel, two-part hinge fitted midway on the steerer and seat tubes. The steerer may paddle either side or switch sides as needed for steering purposes. Steerer tubes come mainly in two common nominal sizes&colon; 1" and 1". A steerer uses calls to direct the paddlers. The steerer may have also carried a short musket and a sword.