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Form Tolerance Spec Table
Form Tolerance KS Specifications — 6 sizes
KS A ISO 1101
Tolerances specifying geometric form accuracy of individual features: straightness, flatness, circularity, and cylindricity.
Practical Notes
- Straightness and flatness are specified without datums. Orientation tolerances (parallelism, perpendicularity) require datums — do not confuse.
- Specifying flatness 0.05 everywhere requires grinding, inflating costs. Relax to 0.1–0.2 for non-functional surfaces.
Selection Guide
Controls individual feature form without datums: straightness, flatness, circularity, cylindricity. Apply to precision guide surfaces, sealing faces, and bearing contacts. Dimensional tolerances alone cannot control form — specify for functionally critical surfaces.
KSForm Tolerance
6 sizes| Name | Type | Symbol | Datum | Definition | Application |
|---|---|---|---|---|---|
| Straightness | Form Tolerance | ⏤ | Not Required | Type | Shaft, , |
| Flatness | Form Tolerance | ⏥ | Not Required | Surface Type Surface | Surface Flat , Surface, Surface |
| Roundness | Form Tolerance | ○ | Not Required | Type Type | Shaft, Bore Single Type |
| Cylindricity | Form Tolerance | ⌭ | Not Required | Type | Cylinder, Shaft Type |
| Profile of Line | Form Tolerance | ⌒ | Type , | ||
| Profile of Surface | Form Tolerance | ⌓ | Surface Surface | 3D Surface, ForbiddenTypeSurface |
Key Features
- No datum required; controls geometric deviation of individual features (lines, surfaces, circles) from ideal form
- Four types: straightness, flatness, circularity, cylindricity; each with independent tolerance zone
- KS A ISO 1101 symbol system; entered in Feature Control Frame (FCF)
Key Applications
Precision guide surface flatness, hydraulic cylinder bore circularity, guide rail straightness, sealing surface flatness
FAQ
What does flatness 0.05 mean?
The difference between the highest and lowest points on the surface must be within 0.05mm. The actual surface must lie between two parallel planes 0.05mm apart.