US Patent 7666048 Method for securing a miniature bulb in a holder

Miniature bulbs are secured in their holders against twisting by first forming holders with tapered cavities smaller at their bottoms than the bulb, then heating the holders to soften them prior to insertion of the bulb. When the bulb is fully seated and the holder has cooled and firmed up, the holder will conform to the exterior shape of the bulb including the irregularities in its surface caused by the bulb formation process. The snug fit of the holder to the irregularities in the bulb resist the twisting of the bulb.