Identifying and determining interchange for bulbs without a part number can be a tricky process.  In this section, we will look at the differences in the 15mm bulb bases.  There are 4 different bases used with the 15mm size.  The two most common bulbs that use these bases are the 1156 and the 1156 bulbs.  If you are unsure of the art numbers for your bulbs, the diagrams below can be used to identify your bulbs.

Note that the pin alignment on the bulbs changes from in line to offset on the sides of the bulbs.  These bulbs do not interchange.  Be sure that you are selecting the correct bulb based on the socket and base type for your application.  Also notice that the positive and negative locations on the bulbs change.