A coupling hook assembly having a hook body defining an enclosed hook pocket with a locking bolt extending from a first aperture in the hook body into operative engagement with a hook jaw to lock and unlock an implement pin for joining a trailer with an agricultural tractor. The locking bolt is pivotally connected with an operating lever mounted on a fixed pivot within the hook body and extending through a second aperture therein. A yoke pivotally mounted on the operating lever is adapted to engage with a notch formed on the external surface of the hook body to secure the locking bolt in the locked position or into engagement with a recess in a part of the operating lever to secure the coupling hook assembly in the unlocked position.