Abstract: A lead-in device is used during installation of a rim-type lock cylinder having a tailpiece in an exit mechanism including a cam having a tailpiece receiving aperture. The lead-in device includes a converging tunnel having an exit aperture sized to match the tailpiece receiving aperture and an entrance aperture that is larger than the exit aperture. The lead-in device also includes a pair of arms positioned to be inserted into the cam aperture to hold the exit aperture in registry with the cam aperture and to maintain the entrance aperture at a predetermined distance from the cam. When the arms are positioned in the cam aperture and the exit aperture is in registry with the cam aperture, the converging tunnel guides a tailpiece inserted into the entrance aperture through the exit aperture and into the cam aperture to engage the cam.