What is the best way of using a hand tool like pliers with Oculus sdk and Unity?

In the Oculus integration package there is a scene called "HandGrabUseExamples" in the folder Assets > Oculus > interaction > Samples > Scenes > Examples. This may give you some idea of how to achieve what your after. They haven't documented the code however so it may take some time to understand what's going on. Here is a very basic break down of the example that may help you. The example uses Interactor scripts on the hands and a Grabbable script and Interactable scripts on the object you wish to use. In this example the interactable scripts are "HandGrabInteractable" and a "UseInteractable" which define the relaxed hand pose and the tight pose for each individual hand and the UseInteractable scripts calls a "ComputeUseStrength" function that does the main processing. (see WaterSpray.cs in the example).