Pliers are a tool added in the AberrationDLC for ARK: Survival Evolved. They allow a survivor to repair items that would typically require a Smithy while away from base, but at a higher resource cost of repairs.
To repair a broken item, open your inventory and drag the Pliers onto the item. The initial repair cost will be the same as in a Smithy, but after the repairing process is completed, another 50% of the initial requirements are required to complete the repair.
If you have enough resources for the initial cost, but not for the second requirement, your item will not get repaired, but your Pliers will still be damaged.