Again not proud of this but as a guy who used to get into fights regularly or rather had fights foisted upon me, just about any blunt object is a great weapon as long as you can grab it and hit your attacker with it.
Honestly people brass knuckles are pretty much just Mall Ninja fodder and no one who took defense seriously unless they knew they would be in close quarters combat with preemptive timing and that they could quickly knock out their opponent would ever have such a thing.
An expanding steel baton however is an incredible weapon, and I think those might actually be legal?
I used to keep a Japanese wooden boken in my car, because I lived in an area where people occasionally got shot and stabbed, and I had it because I had a Mall ninja phase as a teenager. Basically just a large blunt object is probably the best weapon of all.
I swear I’m actually a peaceful guy. I’m the only blacksmith I know in 2 blacksmithing organizations that really isn’t into making knives, when everyone else is. Im a weird worldly nerd, it explains a lot.