Gun Nut (Fallout 3)

Gun Nut is a Fallout 3 and Fallout 4 perk.

Fallout 3
Each of the three ranks of this perk permanently increases the player character's Repair and Small Guns skills by five points.

Fallout 4
In Fallout 4, Gun Nut returns as a feature to allow modifying guns, and also enables the player to build turrets in their settlements.
 * Rank 1: You gain access to Rank 1 gun mods.
 * Rank 2: You gain access to Rank 2 gun mods.
 * Rank 3: You gain access to Rank 3 gun mods.
 * Rank 4: You gain access to Rank 4 gun mods.