Zac Runes explained
There's one set of runes for Zac on patch
11.19
that is the clear favorite for LoL players and pros alike. The best Zac Runes on the position 
Jungle are Resolve as the primary path and
Precision as the secondary path with a pick rate of 68%. Besides runes you should take a look on Zac Build and if you are interested in pro matches take a look at Zac Probuilds. If you want to discuss
Zac then you should visit the champion subreddit.
Primary path on Zac
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
Aftershock is the best keystone rune to run on
Zac. This keystone rune bulks you up, increasing both armour and magic resistance, once you immobilized a champion.
Aftershock synergises both with the sheer amount of crowd control Zac possesses and the need to be tanky as soon as you engage. This is usually followed up by taking
Font of Life,
Conditioning and
Revitalize.
Font of Life provides your teammates with more sustain by healing them whenever they attack a champion whose movement you've recently impaired.
Conditioning powers up Zac tankiness after the laning phase.
Revitalize inceases heals and shields you distribute or receive.
Secondary path on Zac
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
Legend: Tenacity and
Triumph.
Zac gains extra Tenacity with every additional stage of
Legend: Tenacity.
Triumph restores on Zac a part of missing health and award bonus gold, if a champion is killed.