Source Core Rulebook pg. 283 4.0
You can use this weapon to Grapple with the Athletics skill even if you don't have a free hand. This uses the weapon's reach (if different from your own) and adds the weapon's item bonus to attack rolls as an item bonus to the Athletics check. If you critically fail a check to Grapple using the weapon, you can drop the weapon to take the effects of a failure instead of a critical failure.

Monk Unarmed Attacks

Gorilla Slam, Shadow Grasp


Combat Grapnel, Fangwire, Gill Hook