Every physical object is three-dimensional. A hole is a void in a three-dimensional object and may be of any size or shape. A perfect round hole is a cylindrical surface that extends between and is normal to the front and back surface of a substrate sheet. Further, a round hole generates a circular void in the front surface and a circular void in the back surface of the substrate sheet. There are many parameters to consider when specifying or describing a hole.
For the sake of discussion, let us reflect upon the characteristics of a round hole, as described above. In the micro-dimensional real world, the absolutely perfect round hole is difficult to achieve. Thus, we must consider how the round hole may deviate from perfection. The ends of a cylinder describe flat surfaces that are a circular, parallel to each other and normal to the axis. The hole entrance and exit apertures may not be circular, they might be oval or irregular in shape.
- If the front and back surfaces of the substrate sheet are not parallel to each other, the cross section of the hole cylinder is trapezoidal in shape.
- If the hole is not drilled at the normal to the surface of a parallel surface substrate sheet, the cross-section of the hole cylinder describes a parallelogram.
- If the hole entrance circle diameter is different than the hole exit circle diameter, the surface extending between them (the hole wall) is a section of a cone.
