It is in tolerance if all points on the surface lie within the tolerance zone of 0.05. In Figure 2, the surface being measured is shown in red. Figure 2: Surface Flatness Tolerance Zone Figure 2 shows the tolerance zone for the surface flatness called out in the drawing in Figure 1. The flatness tolerance zone is a 3D tolerance zone, meaning that when you are checking flatness of a surface, you are checking the amount of variation up and down the y-axis over the entire plane. Figure 1: Flatness of a Surface on a Drawingįlatness of a surface is merely defining how flat a surface feature must be and is the condition of being purely planar.

Noticing the flatness symbol’s placement is critical in determining whether the flatness requirement is for a surface or a feature of size (FOS). As you can see in Figure 1, the surface’s flatness requirement is not in line with the size dimension. On a drawing, the flatness callout can point straight to the surface with a leader arrow or be extended out from the surface and away from the feature of size. Surface flatness is the type of flatness that most people are familiar with.

Flatness symbol