Single cell flashlight

A single cell flashlight which comprises a barrel (76), a tailcap (78), a head assembly (77), and a semi-permanently mounted reflector (80), lens (26A) and o-ring (79) within the head assembly; which may be switched on and off by rotation of the head assembly with respect to the barrel; which may be focused upon further rotation of the head assembly with respect to the barrel; which may be used as a source of unfocused, substantially spherical illumination by removal of the head assembly from the barrel; which may be provided with a lanyard or a key ring holder positioned near the head end of the flashlight to provide for simultaneous illumination of a lock as well as its key with one-hand operation of the flashlight; and which is provided with a special tailcap insert (64A) for that a single-cell flashlight employing batteries of a "AAA", "AAAA" or special size batteries.