If you're focusing on the tool aspect:
* Repair tool: Something used to fix or mend, like a hammer, screwdriver, or glue.
* Peaceful instrument: Something used for creating or fostering harmony, like a musical instrument or a paintbrush.
If you're focusing on the destructive aspect:
* Peacemaker: Someone or something that promotes peace and understanding.
* Reconciler: Someone or something that brings people or groups together after a conflict.
* Unifier: Someone or something that creates unity or agreement.
If you're focusing on the size aspect:
* Large axe: A larger and heavier tool used for chopping wood.
Ultimately, the best antonym for "hatchet" depends on the specific context and meaning you want to convey.