TamZec is a legendary Runeword created by combining a Tam Rune of Ritual and a Zec Rune of Invocation.
How to Create TamZec
You can create TamZec by adding the legendary Tam Rune of Ritual and the rare Zec Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
TamZec can not overflow because the amount of Offering you receive from the Tam 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