The small zipties I use were fine for my Brahma, they fit between the feather shafts, but she was not that heavily feathered.This thread brings a question to mind. If using leg bands or zip ties, do you put them on differently for feather legged birds? My Cochins have such heavy feathering, I'm not sure I would see the band without having to pick them up and search.
https://www.backyardchickens.com/articles/leg-banding-with-zipties.68075/