P21W vs PY21W vs P21/5W: Automotive LED Bulb Base Guide

Quick answer: P21W, PY21W and P21/5W are automotive bulb designations with different bayonet bases and contact layouts. They are not interchangeable: P21W normally uses a BA15S single-contact base with locating pins at 180°, PY21W uses a BAU15S offset-pin base at 150°, and P21/5W uses a BAY15D dual-contact base.

Before ordering an LED replacement, match the base, pin angle, number of contacts, voltage and the original bulb’s function. This guide helps buyers, installers and OEM/ODM customers avoid a wrong fitment.

Choose the correct P21W, PY21W or P21/5W LED replacement

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1. How to recognize Various Names?

P21W

According to different countries can also be called: BA15S, S25, 1156

 

PY21W

Depending on the country, it can also be called: BAU15S, 1156

 

P21/5W

Depending on the country, it can also be called: BAY15D, 1157

 

Generally there will be different names for different wattages.

Because directional light bulbs often use 21W power, they are also called P21W, PY21W, P21/5W.

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2. How to recognize the difference?

You can compare the difference from the appearance

 

P21W

The two bumps are 180 degrees apart, with a pin angle at the bottom.

 

PY21W

Two bumps 150 degrees apart, one connected pin angle at the bottom.

 

P21/5W

Bumps are usually high and low, with two connected pin angles at the bottom.

What is P21W, PY21W, P21/5W used as?

a. Turn signal

b. Brake light

c. Daytime Running Lights

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FAQ Q&A

How do I confirm my original bulb specification?
Check the owner’s manual, read the marking on the removed bulb, or compare the socket and bulb against a verified fitment chart. For fleet, wholesale or OEM projects, send us the vehicle or application, voltage and a socket photo for confirmation.

What if I ordered the wrong base?
Do not grind, bend or modify the locating pins. Use the correct bulb base, or a purpose-designed adapter only when it has been verified for the socket, voltage and heat clearance. Modifying a bulb can compromise retention, electrical contact and road-safety compliance.

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