BA15s vs BA15d: What Is the Difference?

Compare BA15s and BA15d bayonet bases for specialty bulbs, including contacts, pin layout, replacement checks and RFQ notes.

Direct answer

BA15s is a 15 mm bayonet base with a single bottom contact, while BA15d uses the same general bayonet diameter with two bottom contacts. They are not automatically interchangeable. Confirm the contact count, pin height, voltage, wattage and lamp length before replacement.

Applicable to: For B2B replacement, sourcing and custom lighting projects. Confirm final fit, performance and commercial terms against the exact product specification.

Last reviewed 2026-07-19Technical review: AOTENG Lighting technical sourcing teamEdited by AOTENG Lighting editorial team

Direct answer

Comparison table

Point	BA15s	BA15d
Bottom contacts	Single contact	Double contact
Common use	Single-circuit indicator, signal or vehicle bulbs	Dual-contact or isolated-contact indicator, marine or equipment bulbs
Interchangeability	Do not replace with BA15d unless the socket is designed for it	Do not replace with BA15s when two contacts are required
Must confirm	Voltage, wattage, pin layout and glass size	Voltage, wattage, pin layout, contact function and glass size

How to identify

Look at the bottom of the old bulb and count the solder contacts.

Check whether the bayonet pins sit at the same height or have an offset arrangement.

Read any printed voltage and wattage before choosing a substitute.

Measure the glass diameter and overall length if the bulb fits inside a tight lens or fixture.

Buyer checks

Send a photo of the base and bottom contacts with the RFQ.

Confirm whether the socket needs one circuit or two contacts.

Match voltage and wattage to the equipment label or old sample.

Confirm by RFQ when the old lamp marking is incomplete.

Confirm by RFQ

AOTENG can help compare a sample or photo, but final suitability depends on the socket, circuit, voltage, wattage and fixture space. Confirm by RFQ before bulk ordering.