The Lander Frame Screw has the super important job of keeping the frame of the knife securely fastened. It lives underneath the scale in a lovely pocket that you won't be able to see when the scale is on. It's a T6 head, and the part number is P0056.
We recommend adding a drop of Blue Threadlocker to the screws when reassembling your knife. This will prevent your screws from sneakily escaping into the abyss.
You're going to need a T6 bit and driver to reassemble. We gotchoo'. Try this torx tool with Wiha bits. It's our favorite.