In POE2, the third socket on a weapon is typically unlocked by using a Vaal Orb on it, with a chance to add the extra socket randomly. The catch is that it corrupts the item, so the outcome is risky and not guaranteed.

For skill gems , the third socket comes from a Lesser Jeweller’s Orb, which upgrades a 2-socket gem to 3 sockets. Higher tiers of Jeweller’s Orbs then add more sockets afterward.

What to do

  1. Check whether you mean a weapon/gear socket or a skill gem socket.
  2. For a weapon, use a Vaal Orb and hope for the 3-socket outcome.
  1. For a skill gem, use a Lesser Jeweller’s Orb on a 2-socket gem.

Important note

Vaal-corrupting an item can make it worse, so most players only try it on a spare or on gear they were already willing to gamble with.

TL;DR: weapon = Vaal Orb gamble; skill gem = Lesser Jeweller’s Orb.