Heart of the Oak is a Diablo II: Resurrected runeword made in a 4-socket base. This listing is made in a Flail.
The recipe
Ko + Vex + Pul + Thul — 4 sockets, in staves and maces. The runes must be inserted in that order, into a base with exactly that many sockets.
Buying the finished item means you do not have to source the runes or the base yourself.
Why the base matters
The same runeword in a different base is a different item: the base sets the speed, the requirements and the damage or defense the runeword builds on. Where a runeword has variable stats, the roll you are buying is stated in the item name.
Ladder and Non-Ladder. This item is sold for both realms. Pick your mode above; the two are delivered on different realms, so a single order covers one of them.
How delivery works
This is an in-game item for Diablo II: Resurrected. We meet your character in a game on your realm and trade it to you. You give us your BattleTag at checkout; we never ask for your account password.

