How do brass knuckles work? And I've always wondered if they would slip off in the middle of fighting someone or just plan punches.
Often, there’s a weighted grip behind the rings, which rests in the user’s palm and can be held in place with their thumb. In the absence of that, they still have their fingers wrapped around the the weapon. The only real risk of it falling off would be if they opened your hand, which kind of defeats the purpose of using brass knuckles in the first place.
Brass knuckles are intended to shield the user’s fingers and add some weight to the hand while punching.
If you really want to experiment with the mechanics of brass knuckles staying on your hand, you can use an empty key ring. Slip it over a finger, make a fist, and observe how the ring is held in place. The only difference is that brass knuckles are larger, heavier, and cover all your fingers. Depending on the design, they may be a single loop, or four welded rings. Either way, it’s not going to fall off under normal circumstances.
Also, probably worth remembering, you don’t really, “wear,” them. Brass knuckles are a weapon. You take them out when you’re going to use them, and put them away when you’re not. They’re not designed to be worn on the hand at all times.
There are weapons designed to assist with open hand strikes. Off-hand, some variants of the bagh nakh come to mind. These mount a row of small blades across the palm. You wouldn’t want to punch someone while wearing them, just like you wouldn’t want to palm strike someone while wearing brass knuckles. These weapons have specific roles, which enhance, but also, limit your attack options.