For the 2003 Chevrolet Blazer, the supplied fitment data lists a 9005 bulb for the high-beam headlight. No low-beam bulb is provided, so confirm the low-beam application against the original bulb before ordering. The fog light uses an 881 bulb.
Other notable exterior applications include 3157 for the front turn signal and parking light, 3156 for the reverse light, and 3057R for the brake and tail lights. The rear turn signal uses 3057, while the center stop light is listed as LED.
For illumination and interior locations, the license plate, ash, glove-box, and some map-light applications may use 194 or 7441. The dome light requires comparison with the original bulb: it may be 562 or 564. Map lights may also use 212-2. Check the original bulb where multiple options are listed, particularly for dome and map lights.