Are you talking about the bulb itself, or the entire housing? The bulb itself twists into the housing. If it's not operating right it's due to a wrong replacement, or a dead filament. Yes, it's dual filament. Parking/running lights is the usual term I've heard. If you're replacing the entire housing, pull the entire bracket off with the headlight lens since it's way easier, then take the turn signal lens off and replace.