Is this the correct vane for your system?
The newest Davis anemometer has a D-shaped (in cross section) shaft on the anemometer head. Older anemometers have a round (in cross section) shaft. You must make sure that the replacement vane fits the shaft on your existing anemometer head.
7906L or 7906: This vane is for use on a D-shaped wind vane shaft.
7904: This vane is for use on a round wind vane shaft.