Ruger manufactures several "convertible" models that ship with both a .22 LR cylinder and .22 WMR cylinder, allowing the use of both cartridges. The .22 Short and .22 Long cartridges can also be fired in the Long Rifle cylinder. For those models that ship with both cylinders, the last 3 digits of the serial number are engraved on the front of the cylinder; only cylinders that have been properly timed should be used with any given revolver. The term Super Single-Six refers to those models which have fully adjustable target sights.