Monks of the Way of Wu Xing harness and channel the Five Elements. In Wu Xing, metal is one of these elements and that is exemplified in the mastery of versatile weapons. These weapons then becomes the focal point through which the other elements are channeled.

Path of Wu Xing

When you choose this archetype at 3rd level, your special martial arts training leads you to master the use of certain weapons and channel the elements through them.

Versatile Monk Weapons. Choose one type of weapon: battleaxe, longsword, or warhammer. You gain proficiency with that weapon if you don't already have it. Weapons of the chosen type are monk weapons for you. When you reach 6th and 11th level in this class, you can choose another weapon type from the list.

Channel the Elements. As a bonus action you can channel the elements through your monk weapons. Choose one: acid, cold, fire, lighting, or thunder. Your next hit with a monk weapon does additional damage equal to your Martial Arts die of the damage type you chose. Channeling the Elements requires concentration, as you would concentrate on a spell.

Flurry of the Elements. When you use your Channel the Elements feature and your Attack action with a monk weapon in the same turn, you can spend 1 ki point to make one unarmed strike as part of that same Attack action.