Fiddlesticks Runes explained
There's one set of runes for Fiddlesticks on patch 15.4 that is the clear favorite for LoL players and pros alike. The best Fiddlesticks rune paths on the position 
Support are 
Sorcery as the primary path and 
Inspiration as the secondary path with a pick rate of 44%. Besides picking runes on Fiddlesticks you should learn how to play Fiddlesticks and if you are interested in pro matches take a look on how a pro builds Fiddlesticks. If you want to discuss 
Fiddlesticks then you should visit the champion subreddit.
Fiddlesticks runes from primary path
Sorcery empoweres abilities of Fiddlesticks and increases the available champion resources. Most of high elo players – and our LoL pros in the the major regions – have agreed that Arcane Comet is the best keystone rune to run on Fiddlesticks. This keystone rune adds more damage to your abilities and increases your power in the laning phase. Other primary runes on Fiddlesticks are Axiom Arcanist, Celerity and Scorch.
Axiom Arcanist grants you a shield, as soon as Fiddlesticks gets hurt by alot of magic damage. This rune will help you alot to survive against ability power champions with a lot of burst damage. Celerity boosts all movement speed bonuses to Fiddlesticks. Scorch increases your control in the early game.
Fiddlesticks runes from secondary path
When it comes to your secondary path, most Fiddlesticks players prefer to go with Inspiration. Inspiration opens creative opportunities on Fiddlesticks troughout the match. On the Inspiration path, the best runes for Fiddlesticks are 
Cosmic Insight and 
Biscuit Delivery.
Cosmic Insight grants summoner spell and item haste. Biscuit Delivery is a great rune for laning as it gives additional health and mana, which can help in more aggressive lanes.
FAQ for Fiddlesticks Runes
Which is the best keystone rune on Fiddlesticks?
The best keystone rune on Fiddlesticks is Arcane Comet. This Fiddlesticks runes setup is then referred as Fiddlesticks Arcane Comet.
What runes does Fiddlesticks use?
Runes from the paths Sorcery and Inspiration are the most used runes on Fiddlesticks. For the exact pick rates of Fiddlesticks runes used, you have to study the rune distribution presented.