Cylinders are required to be inspected annually both externally and most importantly internally. External inspection is easy, looking down the small neck opening without something to properly illuminate the interior of the cylinder is impossible without a cylinder inspection light. This 110 volt tank inspection light is 10" x 1/2" (25.4 cm x 1.3 cm) and has a 50 hour life expectancy. Easy to use and will illuminate the entire interior of the cylinder. Light has a rotating on/off in-line switch so you can turn it on only after you insert it into the tank saving the bulb life replacement bulbs not available.