Ahh.Yes, but the only stainless bit on the 221 bolts are the pressed cap:
View attachment 48963
VS the zinc plated ones I use aftermarket:
View attachment 48964
You can use a 17mm socket on them, but over time, it deforms the steel cap on the bolt, that makes the "Star" pattern and they get stuck.
Which is annoying, as when you have the right star socket, they also get stuck once deformed.
Once again, a cost saving measure, stainless steel cap instead of galvanised or phosphated bolts that don't rust.