This step and the next one list the optional tools that can be helpful during assembly. You can build the Bear frame perfectly without them.

Sorry for this extra list, we love tools...

A long caliper of 200mm or more helps to align the Y axis smooth rods spacing on any "Prusa type" printer.

A general purpose clamp will facilitate the squaring of the frame when using a machinist square.

Tweezers are always useful :)

You can add a dab of blue Loctite #243 to the screws during assembly to prevent them from unscrewing.

An 8mm drill bit or 8mm reamer can be useful in case the smooth rods holes on Z axis are a bit too tight.