Various harmonium models can have a different number of stops and drones available. The usual design is however that the stops are bigger knobs and the drones are smaller.
Please take a look at my other harmonium-related channels:
Harmonium Help (Instagram):
https://www.instagram.com/harmoniumservice/
Harmonium Melodies (educational):
http://www.youtube.com/c/HarmoniumMelodies/videos