Weapon Kits allows the player to customize most weapons with attachments and camouflages, in addition to features exclusive to specific games such as paintjobs in Black Ops III, and prototype weapons in Infinite Warfare. Weapon Kits mean that if a specific weapon is received from any method, the Weapon Kit customization will be used for that, allowing for specifically tweaked weaponry. Attachment slots are unlocked via the Weapon Level system, with attachments being unlocked in the same method.
Within Call of Duty: Black Ops III, not all weapons that were added through the update were added to the Weapon Kit system, while the systems in the future titles had their additional weapons added to the system.