If you don't take these little halogen bulbs for desktop lamps with you to the store, you'd never get the right size. That's what I did. That's what I didn't. I didn't take the burnout halogen bulb with me to the store. The two pins on the bottom of the bulb are spaced a few millimeters apart on different wattage bulbs and they won't fit. It's not as simple for example as the bulb in the olympic torch. So I left the store empty handed knowing that it'll entail a second trip to the store later. Done it before too. However, as things would have it, while I was pulling the old halogen bulb out of the desktop lamp, the bulb lit up. So I guess it wasn't plugged in snug enough.