Sockets

Sockets are plain holes in an item. They hold runes (Runes). All sockets on an item are equal and filled in order. Spells use glyphs instead (Glyphs).

Which items. Weapons, bows and crossbows, wands and rods, shields, helmets, body armour, legs and boots. Spellbooks, rings and amulets have no sockets.

Maximum sockets

Item	Maximum
Body armour, two-handed melee, bows, crossbows	4
Shield, one-handed melee, wand or rod, helmet, legs	3
Boots	2

An item also needs enough item level for each socket: 1 socket from item level 1, 2 from 10, 3 from 25, 4 from 40 (Item level).

Getting sockets

Drops. Normal equipment sometimes drops with sockets. Most pieces have none. Magic and rare drops never have sockets.
Jeweller's Orb. Rerolls the number of sockets of an item that holds no runes. It can lower the count as well as raise it, and it is the only way to add sockets. It does not change rarity or affixes.
Lion caches in the atlas yield pre-socketed Normal bases (Lion Caches (Drume)).

A 4-socket body armour costs on average a dozen Jeweller's Orbs, so players buy good pre-socketed bases.

Other orbs. Orbs of Transmutation, Alteration, Alchemy, Chaos, Scouring and the rest never add, remove or reroll sockets or runes. A Vaal Orb keeps them, except on a runeword item (Corruption and the Vaal Orb).

Corrupted items cannot gain sockets or runes.

Choosing between rare and runeword. A runeword needs a Normal base, so a rare's six affixes are the price of a word. See Runewords.