LED previx on bulbs? "rg921, C921 etc

I upgraded to LED bulbs last year. Here's a link to my project:
LED upgrade

The 921 is one of the brightest in a series of 9XX bulbs with the T10 wedge base. If you are thinking of buying LED equivalents, some sellers advertise their light as a replacement for 921 but the only resemblance is the base. You need to make sure it is as bright. 18 5050 leds or 36 3528 or 1210 leds should be about the same brightness

There is also the matter of color. Warm white is color of incandescent lights.

BTW, all leds are made in China. If you buy from most USA sellers you will pay much more than if you buy on eBay from a Chinese seller. There is quite a lot of variation between sellers on eBay. Buy 1 or 2 for a test.

The "C" is an early shape type. It originally stood for Pinecone.

he 921 refers to the size of the bulb. The prefixes denote model number. More than you ever wanted to know about illumination is at Dons bulbs.

For LED replacements, you'll want to know the base number and possibly, the amperage rating of the fixture. The latter is not typically important as the LED replacement will draw 1/5 Amps of the incandescent it replaces. I only mention it because you may decide to use 6 Cree high-watt LEDS in your fixtures to approximate a high power flashlight. That could exceed the rating of the fixture.

Your 921 base size is T5/T10 wedge.