PoE2
Fork
Support
Projectile
Cost Multiplier: 120%
Requires: Level 1
Support Reqirements: +5 Dex
Supports projectile skills, making their projectiles fork.
Projectiles from Supported Skills Fork
Projectiles from Supported Skills deal 50% less Damage after Forking
Place into a Skill's Support Gem socket in the Skills menu to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
PoE1
Fork Support
Support
Projectile
Level: (1–20)
Cost & Reservation Multiplier: 130%
Requires: Level (31–70), (52–111) Dex
Supports projectile skills, making their projectiles fork into two projectiles the first time they hit an enemy and don't pierce it.
Projectiles from Supported Skills Fork
Supported Skills deal (-9–10)% less Projectile Damage

Additional Effects From Quality:
Supported Skills deal (0–10)% increased Projectile Damage
This is a Support Gem. It does not grant a bonus to your character, but to skills in sockets connected to it. Place into an item socket connected to a socket containing the Skill Gem you wish to augment. Right click to remove from a socket.