YaxZec is a rare Runeword created by combining a Yax Rune of Ritual and a Zec Rune of Invocation.
How to Create YaxZec
You can create YaxZec by adding the magic Yax Rune of Ritual and the rare Zec Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
YaxZec can not overflow because the amount of Offering you receive from the Yax Rune exactly fills the required Offering of the Zec Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.
Legions
Helltide