Shapes and the feeler gauge
Pro-Tip. A cone has a round base. A pyramid does not. A feeler blade's mark is its thickness.
Know these by description, not just by picture. Square: four equal sides and four right angles. Rectangle: four right angles, opposite sides equal. Triangle: three sides. Circle: every point the same distance from the center. Cube: six square faces. Cylinder: two circular ends and straight sides. Cone: a circular base that comes to a point. Sphere: a ball. Pyramid: a polygon base and triangular faces that meet at a point.
A cone and a pyramid both come to a point. The cone’s base is a circle. The pyramid’s base is not.
A feeler gauge is a set of thin blades marked with thickness. You use it for a small gap, such as a valve clearance. A tape or ruler is for longer lengths. Read the mark the edge actually lands on, including the fraction. If the part does not start at zero, subtract the starting mark from the ending mark.
Worked example
Two circular ends and straight sides.
That is a cylinder. If it comes to a point, it is a cone.