I currently own three of these . they be great flashlight to have around . they be bright enough to get most job do , small enough to carry just about anywhere , and durable enough to take a beating . sure surefire flashlight be brighter but they be not as durable . I have even hear of people use these as self defense weapon . really heavy abuse may result in a very short bulb life but it carry a spare so you 'll have light again in no time .  as far as the thread and o-ring go , a small amount of Vaseline apply to the thread will keep both the thread and the o-ring lubricate .