Just A Hand is a Melee "weapon" introduced in the 10.1.0 update. It has no upgrades and can be used only in Sandbox mode.
It is a hand with a black glove in the armory, but when using it, it is technically what your hand looks like.
It is not a usable weapon in any game mode other than Sandbox mode, since it doesn't inflict any damage. When a player equips it, nothing is shown but the avatar without any items in their hands. It is meant to be a way to interact with other players, just like the other weapons made for Sandbox. When the user attacks with it, it makes a punching sound with a player's hand showing for less than a second.
It is the only "weapon" in the game with 0 lethality.
It is only shown in the Armory if a player checks it in a Sandbox server.