Originally Posted by 07SPORT
whats the difference in 3157 and 3156, and 3457? always wandered
3156 is single filament for apps like backup lights or dedicated turn signals.
3157 is dual filament for apps like combination stop/tail or a front parking/turn combo.
3457 is the same style bulb as a 3157 with the same base. However, the design current through the individual filaments is different for different applications. There is a large family of bulbs like this of the form 3x57 and 4x57.
Companies that sell LED bulbs often group these bulbs together and offer a single "one size fits all" replacement for all of them.