Adam Savage's Favorite Tools: Machinist Squares
Everyone has some kind of 90-degree angle square in their shop, but Adam advocates for a specific kind of square: the 4” machinist’s square. They allow for fine and delicate layout on small parts, something a big honking 12” square will have trouble with. Adam has them in multiple sizes going down to 3/4” long (super tiny!) but if you had to have only one, get the 4”!