Titus bracer (5e Equipment)
From D&D Wiki
This item first appears to be two 20cm golden white and black snakes with emerald eyes that wraps around your forearm. When activated as a bonus action, they uncoils and slithers into your hand in the form of a golden spear or dagger. The transformation lasts until you deactivate it as a bonus action. If thrown, the weapon fly back to you as a bonus action.
This item can be used with strength or dexterity.