The device holds the light bulb in place. If you do not tighten the thumbscrew sufficiently, it will loosen and the device will hang on the lamp. According to one review, overtightening can cause cracking. Luckily I pulled the bulb out, but putting in a new bulb wasn't easy. I finally threw my hands up and my wife did it for the first time. One of the other reviews mentioned a broken lightbulb. The answer is potatoes. You put the potato in the lamp changer and spin it. Works great.
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