The wrench is A melee weapon used by the engineer in tf2, that is used to deal 75 damage and upgrade a sentry-gun, dispenser, or teleporters.
The sentry-gun is an upgrade-able building in tf2 that is used to kill enemy players, that can be upgraded through 3 levels.
The Gunslinger is an item in tf2 that replaces the wrench as your melee weapon, and it makes you only able to place mini-sentry.
The Mini-sentry is just that a miniature sentry that is non-up-gradable
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