Most modern pocket knives from reputable companies such as Buck, Spyderco, Kershaw, Benchmade, or Cold Steel will use Torx screws to assemble their knives, including the clip. Some older knives, like Emersons, or the Kershaw Whirlwind I'll be working on, use a Philips screw, and yet others will use small Hex/Allen screws.
Here are some common sizes:
Torx: T5-T10, with T6 and T8 being the most common (these are what my Spydercos use).
Philips: Size 000-0, with 00 being common (this is what our example Kershaw uses).
Hex/Allen: sizes: 1/20", 1/16", 5/64", 3/32", 7/64", 1/8"
I like the Jeweler's drivers the best for working on pocket knives. They allow you to apply pressure and turn at the same time, which I feel offers a more positive engagement and prevents stripping of either the bit or the screw. At work we have a nice set from Crafstman (pictured), but here's my favorite $6 Torx multi-driver, from Husky
. These are also great for working on electronics.
If you're going to be re-bending your clip, you'll also need two sets of pliers. Here I have pictured a set of vice grips and a set of pliers. The vice grips aren't ideal, but work in a pinch. If your clip is painted or you're worried about scratching it, you'll want a cloth or some masking/duct tape to wrap around the clip to protect it.
It's also a good idea to pickup a small tube of threadlocker, to prevent your clip screws coming loose in the future. Red loctite
offers a good balance, keeping the screws secured without welding them in there in case you need to re-bend or reposition later on.