I've got a MH fixture that I bought used about a year ago. It needs a new bulb pretty bad, and I have some for another fixture that I thought would work, but they don't. It's a single ended 250 watt fixture. Here's some pics of the ballast and bulb. I circled a piece that's different on the bulb than the other bulbs I have. Maybe that will help you to tell what kind of bulb I need to buy. That's my question, what kind of bulb to put in this.