Collection: BA15S Bulbs

The BA15S base: what does this designation mean?

BA15S stands for: B for Bayonet (quarter-turn lock upon insertion), A for standard geometry, 15 for the diameter in mm, S for Single contact (1 centered metallic pin). It is one of the most common bulb bases in automotive signaling for decades.

It mainly accommodates:

• The P21W (white, 21W) — turn signals, reverse lights, single brake lights
• The R5W (red, 5W) — rear position lights, marker lights, trailers

BA15S vs BAY15D vs BAU15S: similar bases not to be confused

Three variants of the BA15 coexist — identical diameter of 15 mm but different pins:

• BA15S — 1 centered pin, symmetrical straight lug. Universal for P21W and R5W.
• BAY15D — 2 pins at asymmetrical heights. For P21/5W stop+position double-filament bulbs.
• BAU15S — 1 pin with a 5° offset lug. For PY21W orange turn signals only (color error prevention).

These three bases are not interchangeable despite their resemblance — check the number of pins and their position before purchase.

Available BA15S bulbs

The BA15S range includes P21W and R5W in standard halogen (12V and 24V for trucks), long-life versions (reinforced filament), and LED canbus to prevent hyperflashing on modern vehicle turn signals.