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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We are a company providing LED light products for vehicles, e.g., headlights, light bulbs, turn lights and worklights. We have built a global supply chain from LED manufacturers to terminal clients. Besides, we also furnish LED products of the best quality with customers via Amazon, Ebay, Alibaba Express, Wish and our official shopping platform.
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