Zac Runes explained
There's one set of runes for Zac on patch 14.9 that is the clear favorite for LoL players and pros alike. The best Zac rune paths on the position 
Top are 
Resolve as the primary path and 
Precision as the secondary path with a pick rate of 97%. Besides picking runes on Zac you should learn how to play Zac and if you are interested in pro matches take a look on how a pro builds Zac. If you want to discuss 
Zac then you should visit the champion subreddit.
Zac runes from primary path
Resolve empowers the survivability of Zac and increases the tankiness. Most of high elo players – and our LoL pros in the the major regions – have agreed that Grasp of the Undying is the best keystone rune to run on Zac. This keystone rune gives Zac alot of sustain and helps to force your opposing champion out of the lane. Other primary runes on Zac are Demolish, Second Wind and Revitalize.
Demolish increases your pressure on the enemy turrets. This rune will help you to punish bad roams or backtimings of your lane opponent. Second Wind powers up your sustainablity in lane by healing after taking damage from an enemy champion. Revitalize inceases heals and shields you distribute or receive.
Zac runes from secondary path
When it comes to your secondary path, most Zac players prefer to go with Precision. Precision improves attack and sustained damage on Zac troughout the match. On the Precision path, the best runes for Zac are 
Last Stand and 
Legend: Tenacity.
With Last Stand you deal more damage while you are at low health. Zac gains extra Tenacity with every additional stage of Legend: Tenacity.
FAQ for Zac Runes
Which is the best keystone rune on Zac?
The best keystone rune on Zac is Grasp of the Undying. This Zac runes setup is then referred as Zac Grasp of the Undying.
What runes does Zac use?
Runes from the paths Resolve and Precision are the most used runes on Zac. For the exact pick rates of Zac runes used, you have to study the rune distribution presented.