Threads of War Set gives two lines of max stamina, spell and weapon damage, and a proc condition in the Elder Scrolls Online (ESO):
2 items: Adds 1096 Max Stamina
3 items: Adds 129 Weapon and Spell Damage
4 items: Adds 1096 Max Magicka
5 items: Your Light and fully-charged Heavy Attacks gain 100% Status Effect Chance. The Status Effect is based on the damage type of your weapon.